Pollen aperture morphology in Arecaceae: Application within phylogenetic analyses, and a summary of record of palm-like pollen the fossil

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1 Grana ISSN: (Print) (Online) Journal homepage: Pollen aperture morphology in Arecaceae: Application within phylogenetic analyses, and a summary of record of palm-like pollen the fossil Madeline M. Harley & William J. Baker To cite this article: Madeline M. Harley & William J. Baker (2001) Pollen aperture morphology in Arecaceae: Application within phylogenetic analyses, and a summary of record of palm-like pollen the fossil, Grana, 40:1-2, 45-77, DOI: / To link to this article: Published online: 05 Nov Submit your article to this journal Article views: 1983 View related articles Citing articles: 32 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 21 December 2017, At: 09:42

2 Grana 40: 45± 77, 2001 Pollen aper ture morphology in Arecaceae: application within phylogenetic analyses, and a summary of the fossil record of palm-like pollen MADELINE M. HARLEY and WILLIAM J. BAKER Harley, M. M. & Baker, W. J Pollen aperture morphology in Arecaceae: application within phylogenetic analyses, and a summary of the fossil record of palm-like pollen. ± Grana 40: 45± 77. ISSN For a monocotyledonous family, the Arecaceae possess unusually varied pollen, not only in aperture number and orientation, but also in exine ornamentation. Although the majority of species have monosulcate pollen, 17 aperture types, and 13 exine types, have been described. The family belongs to a minority of monocotyledonous families in which both successive and simultaneous cytokinesis occur. The aperture types that have been described for the Arecaceae can be separated into those associated with successive, and those associated with simultaneous, cytokinesis. Palms have a long fossil record, mainly leaves and pollen, but also fruits, stems, and roots. Flowers have also been recovered. Distinctive aperture and/or exine combinations, in the pollen of some species, have prompted comparisons with fossil pollen taxa, certainly from the Late Cretaceous onwards. Occurrences of various fossil pollen taxa, frequently associated with palms, are reviewed, and their morphologies, particularly aperture characteristics, are compared with those of living palm pollen. The systematic rarity of most palm aperture types places limitations on their value in cladistic analyses. Nevertheless, certain aperture characters are of value, and do contribute to a better understanding of the evolution and phylogeny of the family. The diverences between aperture types and aperture characters are addressed. The seventeen aperture types are described, and the interpretation and use of aperture characters in cladistic analyses of the Arecaceae are discussed. Madeline M. Harley & William J. Baker, The Herbarium, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, UK. M.Harley@rbgkew.org.uk (Manuscript accepted 31 March 2001) The majority of palm species produce simple tectate or semi- traced to microsporogenesis type ( Harley 1999 a; Table II). tectate, columellate, monosulcate pollen ( Harley 1990). This The mono-aperturate condition may be the product of either combination of pollen characters is one of the earliest, and simultaneous, modi ed simultaneous ( Blackmore et al. most frequently recorded, angiosperm-like pollen types in 1987), or successive microsporogenesis. However, Harley the fossil record. It predominates in the monocotyledons, ( 1999 a) demonstratedthat in palms equatorial disulcy results and also occurs in a number of basal dicotyledonous families. from successive microsporogenesis,while tripory is associated Nevertheless, seventeen aperture types ( Table I ) have been with simultaneous microsporogenesis. described for the palms (Harley 1996). Apart from monosulcate Pollen types and pollen characters are frequently confused. (symmetric and asymmetric) pollen, trichotomosulcate Broadly speaking, pollen characters are the component parts (usually associated with monosulcy) and equatorial disulcate of pollen morphological types. Although equally important pollen are also quite common. Monosulcy occurs in all palm in the elucidation of evolution and phylogeny, the practical subfamilies except Nypoideae. Trichotomosulcy occurs in application of pollen morphologicaltypes or of pollen charac- Coryphoideae (rare), Ceroxyloideae, and Arecoideae, while ters divers. Pollen types are sets of all the observed characteristics disulcy is systematically restricted to tribe Calameae (sensu of a pollen grain. In a taxonomic or systematic study Baker et al. 2000) in subfamily Calamoideae. Twelve of the species sharing a similar set of characteristics are said to fourteen genera in the tribe, including the largest palm genus have the same pollen type and are grouped together. This Calamus L., with about 360 species, have disulcate pollen. traditional classi cation of pollen into morphological types Of the remaining thirteen pollen types, many are systematically is a useful device in comparative pollen studies, for example, rare (Harley 1996). in the study of dispersed fossil pollen, or for pollen identiis Aperture number within the family has an interesting cation in a number of disciplines such as archaeology systematic distribution. In subfamilies Coryphoideae, Nypo- or aeropalynology. However, pollen types are not usually ideae, Ceroxyloideae, Arecoideae and Phytelephantoideae informative in cladistic analysis. This is because they refer aperture number is either one or three (rarely two), while in to complexes of characters, and as such are not reasonable subfamily Calamoideae aperture number is either one or two hypotheses of homology. The precise de nition of the indi- (rarely none) but never three. DiVerences in aperture number vidual pollen characters, however, provides a clearer mechanism and orientation between some of the subfamilies have been for the assessment of character change in a phylogenetic Ñ 2001 Taylor & Francis. ISSN

3 46 M. M. Harley and W. J. Baker context. This paper focuses both on the value of aperture However, for monosulcy, equatorial disulcy and trichotomosulcy, types in the interpretation of the fossil record of possible we have taken into account widely accepted views palm pollens, and on the careful de nition of the individual regarding oldest entry into the fossil record. A summary of characteristics of aperture types and their value in phylogenetic the geological age range for records of the fossil genera studies of the Arecaceae. discussed is provided in Table IV. The predominance of simple tectate or semi-tectate, columellate, monosulcate pollen throughout the Arecaceae Systematics and taxonomy of recent palms imposes serious limitations on the de nition of informative pollen characters for cladistic analyses. Furthermore, many The systematic arrangement of Uhl & Drans eld ( 1987) is of the more unusual aperture and exine characters are very followed, with the exception of the calamoid palms where uncommon within the family. Nevertheless, Baker et al. the new classi cation of Baker et al. (2000) is used. We also (1999 a) de ned a set of pollen characters for the family, follow the recommendation of the Angiosperm Phylogeny some of which have proved to be of value in cladistic Group (1998), and use Arecaceae rather than the older phylogenetic analyses of subfamily Calamoideae, aperture conserved name Palmae. number in particular. This paper concentrates on the apertures of palm pollen. A sister paper (in prep.) will address the thirteen types of Taxonomy and synonomy of fossil taxa exine ornamentation and ultrastructure of palm pollen. The Pre Quaternary fossil pollen taxonomy can be confusing, extraordinary variety of pollen aperture con guration found and it is often applied to palynomorphs inconsistently in the Arecaceae is described, a range that is unparalleled by (Harley & Morley 1995). To avoid a plethora of erroneous any other monocotyledonous family ( Harley 1999 a, b). or misleading assumptions regarding aynity with modern Attention is given to the relationship between microsporogenpopollenites, taxa, the use of form genera, for example Monocolesis type and aperture type. The Late Cretaceous and Tertiary is often given preference over genera, which pollen fossil record for the family, with emphasis on aperture incorporate names in current use for example, Palmae- characteristics, is reviewed. The results of the cladistic anagenera pollenites, Sabalpollenites and Mauritiidites. Nevertheless, lysis of subfamily Calamoideae, in which pollen characters that incorporate names in current use are important were included, are discussed. Robust, as well as probably where fossil pollen types can be assigned con dently to erroneous, correlations of fossil pollen with pollen of living family, or even genus. Particularly when this can be used to palms are considered. provide a more discrete grouping of some of the palyno- morphs, which would otherwise be assigned to very large MATERIAL AND METHODS ``catch all genera such as Monocolpopollenites. Sometimes there is overlap or duplication resulting in synonomy: Recent pollen Monosulcipollenites Levet-Carette 1964 is an obligate junior synonym of Monosulcites Cookson ex Couper 1953, because The results in the present paper draw mainly on previously it is more recently published, but uses the same type species unpublished aperture data ( Harley 1996). The sample on as the older published genus (Monosulcites minimus). which the results are based comprises pollen morphology for Palmaepollenites ( Potonie 1951) ex Potonie 1958 is an obligabout 1150 collections (c. 850 species). Micrographs and ate junior synonym of Monocolpopollenites because they too microscope slides are held within the collections of the share the same type species (Pollenites tranquillus). Palynology Unit at the Royal Botanic Gardens, Kew. Dicolpopollis P anzl 1956, is considered by Potonie (Muller Preparation methods have been fully described elsewhere 1968) to have priority over Disulcites Erdtman 1947 ex (Harley 1990, 1996, 1999 a). The material is representative Potonie 1960 ( Muller 1968) since Erdtman (1947) did not of all genera currently recognised for the Arecaceae, Uhl & publish a type species for Disulcites. Nichols et al. (1973) Drans eld (1987); Drans eld ( 1989); Drans eld (1991); addressed problems of application of monosulcate fossil Barfod (1991); Beentje (1994); Drans eld & Beentje (1995 a, pollen genera. The description of Arecipites Wodehouse 1933 b); Henderson et al. (1995). was emended. The tectate exine of Arecipites was re-ayrmed Fossil pollen to distinguish it from the reticulate semi tectate monosulcate Liliacidites Couper 1953, with which it was being confused. The data (Tables III, IV ) are drawn from a wide range of Furthermore, Nichols et al. (1973) include Calamuspollenites published sources, as well as data produced in, and held Elsik in Stover et al. 1966, in the synonomy of Arecipites. within, the Palynology Unit at Kew. Preparation methods Authorities for fossil taxa are included in the bibliography. for the latter have been fully described in Harley et al. (1991); Harley & Morley (1995) and Harley (1997). Databases consulted were the electronic Plant Fossil Record Terminology (1990), version PFR2.2 (Gee & Boulter 1994, Lhotak & The pollen terminology follows Punt et al. (1994), with a Boulter 1995, Boulter et al. 1996), and a card index database: few terms taken from Harley ( 1996), for example: ``distal Genera File of Fossil Spores and Pollen (Jansonius & Hills disulcate, ``equatorial disulcate, ``equatorial diporate, (1976), plus updates to In general, for earliest occurrences ``sub-equatorial diporate, ``apical triporate, ``sub-apical of dispersed pollen, discussed in the text, we have triporate, and ``incomplete zonosulcate. The word used the geological age of the type species ( Table III). ``pollen is considered to be a collective noun, short for

4 Pollen aperture morphology in Arecaceae 47 ± ± ± ± ± ± ``pollen grains, and therefore uses the plural form of the is not recognised, because it is now considered to be an verb, i.e. ``pollen are, ``pollen were etc. aberrant form of a brevi monosulcus. The monosulcus, and to some extent the trichotomosulcus, is diycult to separate RESULTS into types and subtypes. An attempt to do this is upheld, but modi ed from Harley (1996), because diverences in The aperture data are described in two conceptually diverent length and sulcus apex are of value in making comparisons formats (Persson et al. 1994). Primarily the data are pre- with the fossil record of dispersed simple tectate fossil pollen sented as aperture types: a combination of the various grains, for example Harley & Morley (1995). characters that comprise the aperture. This is a particularly informative way of describing the apertures for comparison 1. Symmetric monosulcate (Figs. 1± 5) or identi cation, and applicable to a number of disciplines A single symmetric sulcus with an elliptic or broadly elliptic including, in the present context, comparison with dispersed outline, positioned centrally in the distal polar face of fossil pollen in an evolutionary context. However, we also the pollen grain. Pollen shape: symmetric, or very slightly comment on pollen character de nition for cladistic analyses asymmetric, ellipsoid. Three subtypes are de ned: ( Table V ), with particular emphasis on aperture characters used in a cladistic analysis of the calamoid palms ( Baker Subtype 1A Sulcus length as long axis, usually with et al. 1999a). pointed apices ( Fig. 1). Systematic distribution: Coryphoideae (Corypheae: Thrinacinae, Aperture types (Figs. 1± 97; Table I ) Livistoninae, Coryphinae; Phoeniceae; Borasseae: Lataniinae, Hyphaeninae). Calamoideae ( Lepidocaryeae: Apertures, with the exception of the inaperturate pollen of Ancistrophyllinae). Ceroxyloideae (Cyclospatheae; Cero- Pigafetta, are sulcate, extended sulcate, porate, or zonosulc- xyleae; Hyophorbeae). Arecoideae (Caryoteae; Iriarteeae: ate. Seventeen aperture con gurations (types) are described. Iriarteinae, Wettiniinae; Areceae: Dypsidinae, Cyrtostachy- Aperture types 1, 2, 5, 7, 8, 9, and 11 are subdivided. All dinae, Ptychospermatinae, Arecinae, Oncospermatinae; but four aperture types (1, 2, 5 and 8b) are uncommon or Cocoeae: Butiinae). rare ( Table I). Pollen grain shape is often related to aperture Intermediate types not occurring in tribes or subtribes type, for example monosulcate aperture ellipsoid pollen, listed above: Arecoideae ( Areceae: Iguanurinae: 1A± 2B); trichotomosulcate aperture trianguloid pollen. Shape, par- Geonomeae: 1B± 2B). Phytelephantoideae: 1B± 2B). ticularly of monosulcate grains, ranges from symmetric to asymmetric ellipsoid or pyriform ( Fig. 9); kite-shaped ( Figs. Subtype 1B Sulcus shorter than long axis, usually with 6, 12) or elongate, sometimes oblong ( Fig. 8); symmetric rounded apices (Figs. 2, 4, 5). ( Figs. 1± 5) to asymmetric oblate triangular ( Figs. 11, 49); Systematic distribution: Coryphoideae (Phoeniceae). oblate spheroidal ( Fig. 54) or spheroidal ( Figs. 51, 57, Calamoideae ( Lepidocaryeae: Lepidocaryinae). Arecoideae 61, 91). ( Areceae: Cyrtostachydinae, Arecinae). In the aperture type descriptions that follow, pollen shape Intermediate types not occurring in tribes or subtribes listed for each aperture type is also given. Systematic distribution above: Calamoideae (Lepidocaryeae: Raphiinae: 1A± 4). of each aperture type is summarised as far as subtribal level Ceroxyloideae (Ceroxyleae: 1A± 1B); Hyophorbeae: 1A± 2A). (summarised in Table I ). Full details of genera and species Arecoideae (Areceae: Dypsidinae: 1A± 1B). included in each type are provided in Harley (1996). In some species the monosulcate, and sometimes the Subtype 1C Sulcus broad and wide, or circular ( Fig. 3). trichotomosulcate, apertures range from symmetric to asymmetric, Systematic distribution: Calamoideae ( Eugeissoneae). even the length of the sulcus may range from not as Ceroxyloideae ( Hyophorbeae). long as, to as long as, the long axis of the pollen grain. In these taxa aperture and shape characteristics are a mix of 2. Asymmetric monosulcate (Figs. 6± 12) two subtypes. In the descriptions that follow, ``intermediate A single sulcus with a symmetric to asymmetric elliptic, aperture types are listed separately but included in the closest or broadly elliptic to asymmetric triangular, outline. Symmetrically aperture type. or asymmetrically positioned in the distal face of the pollen grain. Pollen shape: slightly or pronouncedly Changes to aperture types and subtypes in Harley (1996) asymmetric, (sometimes elongate), ellipsoid or oblate asymmetric triangular, pyriform or kite-shaped. Separate states There are a few adjustments to the subtypes de ned in of the asymmetric monosulcate condition are less clearcut Harley (1996). Subtypes 1a and 2a, sulcus as long as long than those for symmetric monosulcate pollen. Nevertheless, axis, equal subtypes 1b and 2b in Harley (1996). Subtypes three subtypes are suggested: 1b and 2b, sulcus slightly shorter than long axis, equal subtypes 1a and 2a in Harley (1996). Subtype 2d is not Subtype 2A Sulcus length as long axis, usually with recognised, as it was based on pollen shape not on a variant pointed apices (Figs. 6, 8, 11). of aperture length in relation to long axis. Aperture type 9 Systematic distribution: Coryphoideae (Corypheae: Thrinacinae, ``Symmetric monoporate becomes ``Symmetric polar monoporate, Livistoninae, Coryphinae, Sabalinae; Phoeniceae; while Aperture type 10 ``Asymmetric monoporate Borasseae: Lataniinae, Hyphaeninae) Ceroxyloideae becomes ``Asymmetric equatorial monoporate. Subtype 12b (Ceroxyleae; Hyophorbeae). Arecoideae (Podococceae;

5 48 M. M. Harley and W. J. Baker Table I. Systematic distribution of aperture types in the Arecaceae. Aperture type COR CAL NYP CER ARE PHY 1. symmetric monosulcate ** * ** ** ** 2. asymmetric monosulcate *** ** *** * 3. extended monosulcate * ** * 4. brevi monosulcate * * * 5. equatorial disulcate *** 6. distal disulcate * * 7. symmetric trichotomosulcate * * ** 8. asymmetric trichotomosulcate * 9. symmetric monoporate * ** 10. asymm. monoporate * 11. equatorial diporate ** 12. sub-equatorial diporate ** 13. apical triporate * 14. sub-apical triporate * 15. incomplete zonosulcate?* * 16. zonosulcate * 17. inaperturate *

6 Pollen aperture morphology in Arecaceae 49 Areceae: Oraniinae, Leopoldiniinae, Manicariinae, Dyps- Subtype 5A ± Both bridges strong, narrow bridge almost idinae, Lemurophoenicinae, Euterpeinae, Roystoneinae, as wide as wide bridge (Figs. 23, 24; 110: 1). Archontophoenicinae, Linospadicinae, Ptychospermatinae, Systematic distribution (including 5A± 5B intermediates): Arecinae, Oncospermatinae, Iguanurinae, Masoalinae; Calamoideae (Calameae: Metroxylinae, Calaminae). Cocoeae: Beccariophoenicinae, Butiinae, Attaleinae, Elaeidinae, Bactridinae; Geonomeae) Phytelephantoideae. Subtype 5B ± Both bridges strong, narrow bridge about two thirds the width of wide bridge (Figs. 25, 26; 110: 2). Subtype 2B ± Sulcus shorter than long axis, usually with Systematic distribution (incl. 5B± 5C intermediates): Calarounded apices ( Figs. 9, 12). moideae (Calameae: Salaccinae, Metroxylinae, Plectoco- Systematic distribution: Coryphoideae (Corypheae: Thri- miinae, Calaminae). nacinae, Livistoninae). Ceroxyloideae (Ceroxyleae, Hyophorbeae). Arecoideae ( Areceae: Dypsidinae, Euterpeinae, Subtype 5C ± Both bridges strong but narrow bridge very Linospadicinae, Arecinae, Iguanurinae; Cocoeae: Attaleinae, narrow ( Figs. 27, 28; 110: 3). Bactridinae; Geonomeae). Systematic distribution: Calamoideae (Calameae: Metro- Intermediate types not occurring in tribes or subtribes listed xylinae, Plectocomiinae, Calaminae). above: Coryphoideae: Arecoideae (Areceae: Malortieinae (2A± 2B), Ptychospermatinae (2A± 2B)). Subtype 5D ± Proportions of narrow and wide bridges as in Subtype B, but narrow bridge fragile (Figs. 29± 31; 110: Subtype 2C ± Sulcus broadly ovate or almost circular 5), sometimes broken, giving the illusion of an extended ellipsoid ( Fig. 10). sulcus. Pollen shape broad, asymmetric. This subtype always in Systematic distribution (incl. 5D± 5E intermediates): Calamcombination with subtype 2b. oideae (Calameae: Salaccinae, Plectocomiinae, Calaminae). Systematic distribution: Coryphoideae (Corypheae: Livistoninae); Ceroxyloideae ( Hyophorbeae). Subtype 5E ± Proportions of narrow and wide bridges as 3. Extended monosulcate (Figs. 13± 18) in Subtype C, but both bridges fragile, sometimes broken A narrow to wide symmetric sulcus, positioned centrally in and separating the grain into two halves, giving the illusion of a zono-sulcus (Figs. 32± 33; 110: 6). the distal polar face of the pollen grain and, extending around the short equatorial axes of the grain onto the Systematic distribution: Calamoideae (Calameae: Salaccinae, proximal face. Always symmetric, although evects of Korthalsiinae, Plectocomiinae, Calaminae). dessication, acetolysis or fossilization may give a super- cially asymmetric appearance to the grains. Pollen shape 6. Distal disulcate (Figs. 34± 39) symmetric, ellipsoid or broadly ellipsoid. Two narrow paired sulci, slightly shorter than long axis, on distal face of grain. Pollen shape ellipsoid. Systematic distribution: Coryphoideae (Corypheae: Livistoninae). Calamoideae ( Lepidocaryeae, Eugeissoneae). Systematic distribution: Coryphoideae (Corypheae: Thrin- Arecoideae (Caryoteae; Areceae: Arecinae). acinae). Arecoideae ( Iriarteeae: Iriarteinae). ± ± 4. Brevi monosulcate (Figs. 19± 22) 7. Symmetric trichotomosulcate (Figs. 40± 42, 44) A single sulcus, very short in proportion to long axis, A radially symmetric, three-armed sulcus. Pollen shape oblate positioned centrally and more or less symmetrically in the symmetric triangular. Trichotomosulcate grains are either distal polar face of the pollen grain. Symmetric or almost exclusive within a sample, or occur together with symmetric symmetric elliptic, or broadly elliptic outline. Pollen shape monosulcate pollen. Although the conditions are inter- symmetric ellipsoid or broad ellipsoid. related, and occur in the same subtribes, there is a diverence Systematic distribution: Coryphoideae (Borasseae: Latanare in the species distribution of the two conditions, and so they iinae). Calamoideae (Lepidocaryeae: Raphiinae). Phytelephantoideae. treated here as subtypes: Subtype 7A Pollen in sample exclusively symmetric 5. Equatorial disulcate (Figs. 23± 33, 110) trichotomosulcate ( Figs. 40± 42). Two sulci extend from the distal to proximal face of the Systematic distribution: Arecoideae (Areceae: Arecinae; grain through the short equatorial axes. The meso-sulcus on Cocoeae: Attaleinae, Elaeidinae, Bactridinae). the proximal face is wider (``wide bridge ) than the mesosulcus on the distal face (``narrow bridge ). Pollen shape in Subtype7B Sample includes both symmetric trichotomosulcate polar or equatorial view is symmetric ellipsoid or broadly and symmetric monosulcate pollen ( Figs. 43, 44). ellipsoid. In fossilised or acetolysed pollen, where the sulcus Systematic distribution: Arecoideae (Areceae: Arecinae; membranes have been ruptured or lost, it is bobbin-shaped Cocoeae: Butiinae, Attaleinae, Elaeidinae, Bactridinae). in polar view (Figs. 29± 31), and in equatorial view, long axis, trapezium-shaped. Five subtypes are de ned ( Fig. 110: 8. Asymmetric trichotomosulcate (Figs. 46± 48) 1,2,3,5,6). If more than one subtype is included in the A more or less radially asymmetric, three-armed sulcus. systematic distribution it is indicated in parentheses. (NB. Pollen shape oblate asymmetric triangular. Asymmetric trichotomosulcate the descriptions of subtypes 5d and 5e have been revised grains may be exclusive within a sample but from Harley ( 1996): this condition is rare, more frequently they occur together,

7 50 M. M. Harley and W. J. Baker ± ± ± ± ± with often extremely asymmetric, monosulcate pollen. How- Harley 1996). This is probably not a stable aperture type. ever, to correlate with the treatment of aperture type 7a, the The descriptions were based on one collection for which two conditions are treated here as subtypes. there were only a few pollen grains. It is probably malformation of a short sulcus. Further material should be examined. Subtype 8A Pollen in sample exclusively asymmetric trichotomosulcate. 13. Apical triporate (Figs. 75, 76) Systematic distribution: Coryphoideae (Corypheae: Thrinacinae). A circular pore is positioned apically at each of the three Arecoideae (Cocoeae: Bactridinae). apices of the oblate triangular grains. Systematic distribution: Arecoideae (Areceae: Arecinae). Subtype 8B Sample includes both asymmetric trichotomosulcate and asymmetric monosulcate pollen ( Figs. 45± 47). 14. Sub-apical triporate (Figs. 77± 82) Occasionally more or less symmetric grains occur in mixed Three circular pores positioned sub-apically on the distal samples ( Fig. 50) where asymmetry predominates. face of each of the three apices of the oblate triangular Systematic distribution: Coryphoideae (Corypheae: grains. Thrinacinae). Ceroxyloideae (Ceroxyleae; Hyophorbeae) Systematic distribution: Arecoideae (Areceae: Sclerospermatinae). Arecoideae (Areceae: Dypsidinae, Malortieinae, Euterpeinae, Roystoneinae, Cyrtostachydinae,Ptychospermatinae, Arecinae, Iguanurinae, Masoalinae; Cocoeae: Butiinae, 15. Incomplete zonosulcate (Figs. 83± 88) Attaleinae, Bactridinae; Geonomeae). Pollen grains circular oblate. The aperture almost encircles the grain, leaving only a short connection (hinge) on presumed 9. Symmetric monoporate (Figs. 51± 57, 59± 61) distal face (Figs. 85, 88). The two halves are equal. Pollen grains with a single pore symmetrically positioned in Systematic distribution: Arecoideae ( Areceae: Arecinae). [In presumed distal pole. Two subtypes are de ned: the pollen of a number of species in Salacca (Calamoideae: Calameae: Salaccinae) and in Korthalsia (Calamoideae: Subtype 9A Pollen grains spheroidal ( Figs. 51± 53, 57, Calameae: Korthalsiinae) the aperture arrangement is weakly 59± 61). equatorial disulcate (aperture subtype 5e), or may be incomplete Systematic distribution: Calamoideae (Lepidocaryeae: zonosulcate or complete zonosulcate (see discussion)]. Lepidocaryinae). Ceroxyloideae (Ceroxyleae). Subtype 9B Pollen grains circular oblate ( Figs. 54± 56). 16. Zonosulcate (Figs. 89± 92) Pollen grains more or less spheroidal. The aperture encircles Systematic distribution: Arecoideae ( Areceae: Arecinae). the grain through the presumed poles. The two halves are equal. 10. Asymmetric monoporate (Figs. 58, 62) Systematic distribution: Calamoideae: (Calameae: Salaccinae, A single pore positioned subequatorially on one of the two Korthalsiinae); Nypoideae. short equatorial axes. Pollen shape ellipsoid. Systematic distribution: Calamoideae (Calameae: Calaminae). 17. Inaperturate (Figs. 93± 97) Pollen grains more or less spheroidal. The pollen wall is not 11. Equatorial diporate (Figs. 63± 68) robust and combined with the spheroidal shape the pollen Two pores symmetrically positioned on opposite sides of the grains are frequently folded or split under pressure. There is presumed equator. Two subtypes are de ned: no evidence of apertures(s) in the acetolysed pollen exine. Subtype 11A Pollen grains more or less spheroidal. Small Systematic distribution: Calamoideae (Calameae: Pigafettinae). to average pores. Pore position with regard to polarity, not established (Figs. 63± 66). Systematic distribution: Calamoideae (Calameae: Korthalsiinae). Microsporogenesis ( Figs. 98± 107; Table II) Microsporogenesis and tetrad type are re ected in the shape and aperture con guration of the mature free pollen. Tetrad data have been demonstrated to be of evolutionary and ± Subtype 11B Pollen grains ellipsoid. Large circular pores positioned on short equatorial axes ( Figs. 67, 68). systematic value ( Harley 1999a). In summary, in the Systematic distribution: Calamoideae (Calameae: Calaminae). Arecaceae all pollen grains are free individuals at maturity. However prior to release, while still in the callose envelope 12. Sub-equatorial diporate (Figs. 69± 74) of the pollen mother cell (PMC) three tetrad con gurations Pollen grains ellipsoid. Two small± average-sized circular occur: tetragonal ( Figs. 98, 100, 105), tetrahedral ( Figs. 99, pores, positioned sub-equatorially, one on each of the short 101, 106) or decussate ( Figs. 102, 107). equatorial axes. Tetragonal tetrads are the result of successive cytokinesis Systematic distribution: Calamoideae (Calameae: Calaminae). in which the cell plates extend centrifugally, while tetrahedral Note: In Mauritia exuosa L.f. (Calamoideae: Lepidocaryeae: tetrads are the result of simultaneous cytokinesis in which Lepidocaryinae) a third form of dipory, distal diporate, with the cell plates advance centripetally. Decussate tetrads occur two small circular pores, paired on the presumed distal face infrequently but, in palms, always as a small percentage of of the grain has been described (Ferguson & Harley 1993; an otherwise tetragonal or tetrahedral sample, and so appar-

8 Pollen aperture morphology in Arecaceae 51 ently could be the result of either successive or simultaneous types that occur in recent palms are found in the fossil cytokinesis. Very rarely, in Washingtonia lifera (Linden) record. The list of names is not exhaustive. Those included H. Wendl. ( Harley 1996), all three tetrad types are observed are, in general, the most commonly encountered, with many in the same plant. falling into the category of 50 or more records. For consist- Mature pollen even after acetolysis often retains an impres- ency ( Table III), the earliest geological record for each genus sion mark on the proximal face of the grain, which can be is taken from the type species. If available in the Plant Fossil used to indicate tetrad type: linear for tetragonal tetrads Record ( PFR2.2) database (1990), the known geological age ( Fig. 104), or Y-shaped ( Fig. 103) for tetrahedral tetrads range (my), and geographic range is given for all records (Harley 1999a). post-dating the type species (PFR ): ( Table IV). Results so far from tetrad studies (and from observations However, pre Cretaceous records ( before c my) of of impression marks on mature pollen grains) show striking fossil genera and species originally described for Late systematic distribution patterns for each of the two tetrad Cretaceous to late Tertiary angiosperm pollen, probably types. The calamoid and nypoid palms, so far examined indicate too broad an interpretation of the original type at PMC stage, have tetragonal tetrads while results so description. Time, however, does not permit careful checking far recorded for the tetrad stage of coryphoid, ceroxyloid, of the hundreds of records involved. arecoid and phytelephantoid pollen are of predominantly An iconographic summary ( Fig. 108), of rst geological tetrahedral tetrads ( Harley 1999a). Results also show a records of aperture types described in the text, based on the remarkable correlation between aperture type and tetrad time scale of Harland et al. (1989), is provided. However, type ( Table II). note that the icons for monosulcy and trichotomosulcy are A). Aperture types associated with tetragonal tetrads placed at earliest entry into the angiosperm fossil record, and probably represent dicotyledons. 1. symmetric monosulcate; 3. extended monosulcate; 4. brevisulcate (symmetric); 5. equatorial disulcate; 10. asymmetric Aperture types 1 and 2: symmetric and asymmetric monomonoporate; 11A & 11B. equatorial diporate. 12. sub- sulcate, ellipsoid pollen equatorial diporate. A) with simple tectate, verrucate or reticulate exine B). Aperture types associated with tetrahedral tetrads Arecipites, type species: A. punctatus Wodehouse 1933; 2. asymmetric monosulcate; 4. brevi-sulcate (asymmetric); 6. Calamuspollenites, type species: C. pertusus Elsik in Stover distal disulcate ( Thanikaimoni 1970); 7. symmetric trichoto- Elsik & Fairchild 1966; Monocolpopollenites P ug & mosulcate; 8. asymmetric trichotomosulcate; 14. sub-apical Thomson in Thomson & P ug 1953, type species M. trantriporate ( Thanikaimoni 1970); 16. zonosulcate. quillus (Pot.) Jansonius & Hills 1976; Monosulcipollenites, C). Aperture types for which tetrad type has not been type species M. minimus Levet-Carette 1964 ( junior synonym demonstrated of Monosulcites); Monosulcites, type species M. minimus 9. symmetric monoporate; 13. apical triporate; 15. incomplete Cookson ex Couper 1953; Palmaepites Biswas 1962; zonosulcate; 17. inaperturate. Palmaepollenites (Potonie 1951) ex Potonie 1958 ( junior synonym of Monocolpopollenites); Palmidites Couper 1953; Summary of fossil pollen taxa which have similar aperture Psilamonocolpites van der Hammen & Garcia de Mutis 1965; characteristics to those found in recent palm pollen ( Fig. 108; Sabalpollenites Thiergart in Raatz Tables III, IV ) B) more sculptured exine The present study focuses on late Cretaceous and Tertiary Clavamonocolpites Gonzalez Guzman 1967; Couperipollis palm-like pollen, where aperture number and con guration, Venkatachala & Kar 1969 (spinose); Echimonocolpites (Sah and also exine composition, have been used to suggest & Dutta) Salard-CheboldaeV aynities with pollen of recent palm species by the authors Gemmamonocolpites Van der Hammen & Garcia de Mutis of the fossil taxa. Inclusion of a taxon in this summary does 1965; Mauritiidites Van Hoeken-Klinkenberg 1964 (spinose not imply, of itself, that the present authors endorse an intectate, with bulges below the spines as in Mauritia aynity with the palms. Rather, this summary from the L.f. and Lepidocaryum Martius (Lepidocaryeae)); Race- published literature provides a starting point for discussion monocolpites (gemmate or clavate) Gonzalez Guzman and revision, sometimes of long-held assumptions. 1967; Spinomonosulcites Singh & Misra There are also some pre- Late Cretaceous pollen types that share some characteristics with palm pollen (see Aperture type 3: extended monosulcate ellipsoid Discussion). However, they often have other characteristics, Arengapollenites Kar 1985 (spinose, intectate); Clavafor example, presence of endexine, that preclude further palmaedites Rao & Ramanujam 1978; Longapertites Van speculation that they might represent ancestral palms. To Hoeken-Klinkenberg 1964 (simple tectate or reticulate); avoid possible confusion they are not listed below, or in Quilonipollenites Rao & Ramanujam 1978, Phadtare & Table III. Kulkarni 1984 (coarsely reticulate). Exine type and pollen wall ultrastructure of modern palm pollen, are the subject of another paper (in prep.). However, Aperture type 5:equatorial disulcate ellipsoid/trapezoid pollen in the following summary of fossil pollen taxa we thought it Calamipollenites Sun Mengrong 1989 (reticulate with polygonal would be useful to give the exine type in parentheses, where lumina); Dicolpopollis P anzl 1956 (reticulate, verwould it has not been implied in the generic name. Not all aperture rucate or granulate); Disulcipollis Krutzsch 1970 (simple

9 52 M. M. Harley and W. J. Baker (For legend see page 53).

10 Pollen aperture morphology in Arecaceae 53 tectate); Disulcites Erdtman 1947 ex Potonie 1960 ( junior in phylogenetic studies. This study describes pollen aperture synonym of Dicolpopollis). characteristics in the Arecaceae. In a broader context the Aperture types 7A and 8A: trichotomosulcatetrianguloid pollen results allow comparison with apparently similar aperture con gurations elsewhere in the monocotyledons. Such comparisons Trichotomosulcites Couper 1953 (simple tectate or reticulate); are valuable in studies of monocot evolution and Jusinghipollis Jansonius & Hills 1987 (microreticulate). phylogenetics ( Furness & Rudall 1999, Harley & Zavada Aperture type 9A: monoporate spheroidal pollen 2000). Within the Arecaceae, some characteristics of pollen apertures have been used evectively in a cladistic analysis of Echimonoporopollis Saxena, Kar & Misra the calamoid palms, while the circumscription of pollen Aperture type 12: sub-equatorial diporate ellipsoid aperture types (combinations of individual characteristics for comparative studies) for living palms has permitted more Diporoconia ( Kedves) Frederiksen 1985 (simple tectate); informative comparison with dispersed fossil pollen. Piladiporocolpites Kar 1995 (gemmate); Psiladiporocolpites Numerous aperture types, mainly based on form, number Kar 1995 (simple tectate); Retidiporocolpites Kar 1995 and position, have been described ( Table I ) for comparative (reticulate). pollen studies. Nevertheless, these types separate into three Aperture type 14: sub-apical triporate trianguloid developmentally related groups: those associated with both successive and simultaneous microsporogenesis, those associated Constantiniporis Belsky, Boltenhagen & Potonie 1965 (simple with successive microsporogenesis, and those associated tectate, reticulate or spinulose); Doreenipites Biswas 1962 with simultaneous microsporogenesis. A fourth less formal (reticulate or granular); Retitrilatiporites Misra, Singh & group comprises aperture types for which data from micro- Ramanujam 1996; Trilatiporites Ramanujam 1966 ex Potonie sporogenesis are incomplete (simple tectate); Victorisporis Belsky, Boltenhagen & Within each of the groups similarities to, or diverences Potonie 1965 (simple tectate). Note that the icon representing from, pollen of other monocotyledonoustaxa are commented subapical tripory ( Fig. 108) is placed in the earliest Miocene, on, and attention is also given to the fossil record for each as the taxa of older records are pollen forms that do not aperture type where relevant. We acknowledge that other appear to show any aynity to palm pollen. pollen characteristics such as ultrastructure and exine topo- Aperture type 15: incomplete zonosulcate spheroidal logy, as well as apertures, must be taken into consideration in any assessment of possible ancestral relationships for Proxapertites Van der Hammen 1956 (simple tectate or palm-like fossil pollen. However, pollen apertures are an reticulate); Retimonocolpites Pierce important aspect of angiosperm evolution, and the palms Aperture type 16: zonosulcate spheroidal over valuable insights into possible evolutionary pathways for a number of interesting aperture con gurations, that are Paravuripollis Rao & Ramanujam 1978 (clavate); also recorded in the fossil record. Spinizonocolpites Muller The aynity of dispersed fossil pollen grains can be diycult Aperture type 17: inaperturate spheroidal to prove, particularly for systematically widespread aperture types, monosulcate in particular. Palm pollen, unusually for Grimsdalea Gemeraad, Hopping & Muller 1968 (clavate, a monocotyledonousgroup, has a propensity for fossilisation intectate). given the right conditions for the processes of burial and fossilisation to take place (Harley 1996). Although this gives DISCUSSION palms ``the edge, in the fossil pollen record for monocotyledons, not all aperture types that occur in the pollen of Pollen grains are microscopic and develop to maturity in a living palms are known from the fossil record. Many of the protected environment that is only indirectly avected by most well-documented were previously discussed by Muller external factors such as climate, habitat and soil type. (1979, 1981). DiVerences in pollen morphology do not necessarily re ect Three of the aperture types described for the Arecaceae obvious diverences in macromorphology,but may lend unexpected may be the result of either simultaneous or successive micros- support to data from other sources for example, in porogenesis: monosulcate (symmetric or asymmetric), brevis- Euphorbiaceae: Zimmermannia (geographic separation: ulcate or monoporate. Of these, monosulcate is very Poole 1981), or Burseraceae (molecular data: Clarkson et al. common, while brevisulcate and monoporate are unusual. in prep.). Therefore, pollen morphological data are of value In fact, the combination of a simple tectate or reticulate Figs. 1± 12. Aperture type 1. symmetric monosulcate; Aperture type 2. asymmetric monosulcate: 1. Chamaedorea elegans Mart., Linden s.n., polar view, distal face, subtype 1A [SEMÖ 3425]. 2, 4, 5. Areca whitfordii Becc., Elmer 16240: 2. polar view, distal face, subtype 1B [SEMÖ 2000]; 4. Polar view, mid focus [LMÖ 1000]; 5. Polar view, low focus [LMÖ 1000]. 3. Tectiphiala ferox H.E. Moore, Vaughan 12580, polar view, distal face, subtype 1C [SEMÖ 1300]. 6. Syagrus sancona H. Karst., Eggers 15681, polar view, distal face, subtype 2A [SEMÖ 3000]. 7. Pritchardia minor Becc., Cranwell et al. 3103, group of grains to show general asymmetry, subtype 2A/2B [LMÖ 350]. 8. Ptychosperma sp., Brass 28089, group of grains to show general asymmetry, subtype 2A [SEMÖ 400]. 9. Attalea maripa (Aubl.) Mart., Britton 494, polar view, distal face of pyriform grain, subtype 2B [SEMÖ 2000]. 10. Chamaedorea pumila H. Wendl. Ex Dammer, N.E. Brown s.n., two grains, polar view, distal faces, subtype 2C [SEMÖ 1600]. 11. Brahea dulcis ( Kunth.) Mart., Sargent s.n., polar view, mid focus, subtype 2A [LMÖ 1000]. 12. Pritchardia minor Becc., Cranwell et al. 3103, polar view, mid focus, subtype 2A [LMÖ 1000].

11 M. M. Harley and W. J. Baker 54 (For legend see page 55).

12 Pollen aperture morphology in Arecaceae tectum, a columellate infratectum and a distally positioned monosulcate aperture is, systematically and in terms of species numbers, the most widespread pollen type in the monocotyledons. It is dominant in the Asparagales, Liliales and Arecales. It also occurs in a number of basal dicotyledons, for example, Magnoliaceae (Praglowski 1974); Chloranthaceae (Chapman 1987), and Myristicaceae ( Walker & Walker 1981, 1983). Simple tectate or reticulate monosulcate pollen are also frequent among dispersed pollen grains recovered from the oldest sedimentary rocks containing angiosperm-like pollen, for example, Doyle (1969); Hughes (1986, 1994); Walker & Walker (1986). Its early entry into the pollen fossil record, combined with its occurrence in the some of the key basal dicotyledonous families, has led to the widely held opinion that it is probably the earliest of angiosperm pollen types ( Kuprianova 1954, Walker 1974, Zavada 1984, Blackmore & Crane 1998 and others). In fact few authors dispute this. Apart from diverences in the con guration of the monosulcus (Nichols et al. 1973) there are other characteristics that are of value in establishing aynity for dispersed simple tectate or reticulate, monosulcate fossil pollen grains. These include exine and ultrastructure. For example, Zavada (1990) suggests an aynity to the monocot genus Barbaretta (Haemodoraceae) for the fossil pollen species Granamonocolpites luisae Herbst 1970, based on a comparable verrucate exine surface, and highly distinctive exine layers. Doyle & Hotton (1991) argue convincingly for a position within the core Magnoliales for Lethomasites, rather than it being representative of a Bennettitalean taxon, because of the typically magnolialean granular layer underlying the tectum. Harley & Morley (1995) described sections of two monosulcate species of Palmaepollenites and demonstrated strong ultrastructural support of a relationship with the coryphoid species Pritchardia paci ca B.C. Seeman and H. Wendl. Palmaepollenites kutchensis Venkatachala and Kar 1969, while the other, un-named, species of Palmaepollenites has ultrastructural characteristics of some of the genera in the arecoid tribe Iguanurinae. Another useful characteristic is presence of an operculum in the aperture: Nymphaea (Moore et al. 1991), Liliales, Bromeliales (Halbritter 1992), or absence of an operculum (Arecales ± this paper). Size may be informative but should be used with care, fossilisation, or acetolysis can cause as much as a 10% reduction in pollen size. Pollen size ranges from about 15 to 90 mm in palms (Harley 1996). Very small pollen grains (<20 mm) are found only in a few species of subfamily Coryphoideae, while the largest (80± 90 mm) are also unusual, occurring only in Borassodendron (also subfamily Coryphoideae), a few 55 species of Attalea (Arecoideae), and some species of Phytelephantoideae. Presence of an endexine usually implies dicotyledonous origin, absence often indicates a monocotyledonous source plant. However, exceptions to this endexine rule are abundant in the basal dicotyledons (Doyle & Hotton 1991) for example, Myristicaceae ( Walker & Walker 1981, 1983). Setting aside Liliacidites Couper 1953, which has a distinctly modi ed reticulum, and is generally considered to be liliaeceous in origin, there are a number of genera used to describe simple tectate or nely reticulate, monosulcate fossil pollen. Of these the most frequently encountered are: Monocolpopollenites and Monosulcites (Table IV ). Monocolpopollenites is usually applied to Late Cretaceous and Tertiary records, while Monosulcites is more frequently used for older pollen whose origins are probably gymnospermous or Bennettitalean (Osborn 2000). Nevertheless, Monosulcites has been widely used for Tertiary monosulcate pollen as well, particularly in India, and the Far East (Harley 1996). A number of monosulcate fossil genera describe exine sculpturing: Clavamonocolpites, Gemmamonocolpites, Spinomonocolpites, Echimonocolpites, Psilamonocolpites. Some of these may well have palm origins. Where pollen can be assigned to the Arecaceae with reasonable con dence the genera Palmaepollenites, Palmaedites, Palmaepites, Arecipites or Sabalpollenites are often used. In their emended diagnosis Nichols et al. (1973) include the curiously named monosulcate Calamuspollenites in the synonomy of Arecipites (Calamus species have pollen with two equatorial sulci). The age ranges for many of the monosulcate fossil genera are extensive (Table IV ), and amplify the complexity of re ning the possible parent plants of many of the fossils recovered. Brevi monosulcate is probably an occasional, and evolutionarily later, modi cation of the plesiomorphic monosulcate state. The fact that only a few genera of palms have species with brevi monosulcate pollen, and the genera are in diverent subfamilies: Borassodendron (Coryphoideae), Eugeissona brachystachys Ridley (Fig. 20), and Raphia (Calamoideae) and Ammandra (Phytelephantoideae) adds support to this supposition. Borassodendron (Fig. 19) and Ammandra (Fig. 21), have notably similar pollen morphology overall: large and with a thick-walled reticulate exine ( long axis 60± 85 mm in Borassodendron, 65± 80 mm in Ammandra, exine 4± 6 mm thick), and present a striking example of parallel evolution. Borassodendronhas a Thailand ± Peninsula Malaysia ± Borneo distribution, while Ammandra occurs only in Colombia and Ecuador (Henderson et al. 1995). The pollen of the predominantly African genus Raphia (Fig. 22) is diverent: smaller ( long axis 17± 33 mm, exine 0.5± 2.5 mm thick) and simple tectate with a highly distinctive ultra- Figs. 13± 22. Aperture type 3. extended monosulcate; Aperture type 4. brevi monosulcate: 13. Eremospatha macrocarpa (G. Mann & H. Wendl.) H. Wendl., Mann 2338, polar view, distal face, aperture type 3 [SEMÖ 2000]. 14, 15. Licuala sp. Chatan et al. 3114: 14. Equatorial view, high focus, aperture type 3 [LMÖ 1000]; 15. Polar view, proximal face, low focus [LMÖ 1000]. 16. Gronophyllum sp. Essig 55167, group of grains to show general appearance of the pollen, aperture type 3 [SEMÖ 900]. 17, 18. Eugeissona tristis GriYth, Holttum 9772, 17. Polar view, distal face, high focus, aperture type 3 [LMÖ 1000]; 18. Whole grain opened out at (frequent state of acetolysed, or fossilised, extended sulcate pollen grains), mid focus, aperture type 3 [SEMÖ 1000]. 19. Borassodendron borneense J.Dransf., Drans eld JD800, polar view, distal face, aperture type 4 [SEMÖ 1000]. 20. Eugeissona brachystachys Ridley, Ridley 16294, mid focus, aperture type 4 [LMÖ 1000]. 21. Ammandra decasperma O.F. Cook, Balslev et al , oblique equatorial-polar view, showing distal face, aperture type 4 [SEMÖ 1700]. 22. Raphia australis Oberm. & Strey, Strey 7493, oblique equatorial-polar view, showing distal face, aperture type 4 [SEMÖ 2800].

13 M. M. Harley and W. J. Baker 56 (For legend see page 57).

14 Pollen aperture morphology in Arecaceae 57 structure (Harley 1996, and in prep.). There are no published records of fossil pollen for Borassodendron, Ammandra or Raphia and, to our knowledge, no fossil Eugeissona brachystachys pollen have been recorded since Muller (1979) noted an absence of any fossil record for pollen of this type. Monoporate apertures are infrequent in palm pollen. It is likely that they too are an occasional later modi cation of the sulcate aperture. Monopory is also uncommon in the monocotyledons (Harley & Zavada 2000) with the major exception of the Poales, where it is distinguished by the presence of an annulus around the pore. Within the Arecaceae the systematic distribution of monoporate pollen is disjunct, but does not re ect the equally disjunct distribution of the brevi monosulcate aperture type: Calamoideae: Pogonotium, Mauritiella; Ceroxyloideae: Ravenea; Arecoideae: Areca caliso Becc. The asymmetric position of the small pore in the ellipsoid pollen of Pogonotium is somewhat anomalous. It would appear to be associated with the equatorial diporate condition, rather than with monosulcy. Similar pollen are produced by Pandanus eydouxii Balf. F. (Huynh 1991). However, the enlarged wall structure surrounding the single pore in P. eydouxii is not present in Pogonotium. Mauritiella is the only genus of the South American subtribe Lepidocaryinae to have porate pollen. Mauritia and Lepidocaryum both have monosulcate pollen. Mauritia or Lepidocaryum ± like fossil pollen, Mauritiidites, are recorded from South America, India and Africa, but so far not porate Mauritiella-like pollen. The distinctive spiny intectate pollen, and lamellated ultrastructure, have recognisable similarities between the three genera, and are unique Figs. 34± 39. Aperture type 6. Distal disulcate: 34, 36a-c. Chamaerops humilis L.: 34. Moris s.n., polar view, distal face [SEMÖ 3300]; 36a, 36b. Drans eld 4461: 36a. Polar view, mid-focus to demonstrate the unusual occurrence of this aperture type in a collection with predominantly distal disulcate pollen [LMÖ 800]; 36b. Polar view, low focus, more frequent distal disulacte pollen from same collection as 36a [LMÖ 800]; 36c. Brummitt & Ernst 5936, group of pollen grains to show general appearance [LMÖ 300]. 35, 37± 39. Iriartella setigera (Mart.) H. Wendl., Moore et al. 9501: 35. Polar view, distal face [SEMÖ 4600]; 37. Polar view, high-mid focus [LMÖ 1000]; 38. Equatorial view, short axis, mid focus [LMÖ 1000]; 39. Polar view, low focus [LMÖ 1000]. Figs. 23± 33. Aperture type 5. equatorial disulcate: 23, 24. Calamus elopurensis J. Dransf., Kadir A2651: 23. Oblique equatorial-polar view, showing distal face, subtype 5A [SEMÖ 3150]; 24. Polar view, proximal face, subtype 5A [SEMÖ 3430]. 25, 26. Calamus convallium J. Dransf., Drans eld JD6136: 25. Polar view, distal face, subtype 5B [SEMÖ 3000]; 26. Polar view, proximal face, subtype 5B [SEMÖ 2530]. 27, 28. Calamus deerratus G. Mann & H. Wendl., Tuley 846: 27. Polar view, distal face, subtype 5C [SEMÖ 2900]; 28. Polar view, proximal face, subtype 5c [SEMÖ 2900]. 29± 31. Plectocomia elongata Mart. Ex Blume, Curtis 2436: 29. Polar view, distal face, high focus, subtype 5D [LMÖ 1500]; 30. Polar view, mid focus, subtype 5D [LMÖ 1500]; 31. Polar view, proximal face, low focus, subtype 5D [LMÖ 1500]. 32. Salacca clemensiana Becc., Clemens 26380, Polar view, distal face, note fragility of ``bridge, subtype 5E [SEM x 2000]. Salacca aynis GriYth, GriYths 6429, pollen grain where the fragile ``bridges on the distal and proximal polar faces have broken, and the grain is in two halves, subtype 5E [LMÖ 1000]. among the monocotyledons. The very thick-walled oblate monoporate pollen of Areca caliso is unusual. No other examples within or outside the Arecaceae, are known. The fossil form genus Echimonoporopollis (Saxena et al. 1992) shows some similarity to the pollen of Ravenea (Figs. 57, 59± 60). Ravenea is a Madagascar endemic, while records of

15 M. M. Harley and W. J. Baker 58 (For legend see page 59). Echimonoporopollis are from the Neyveli Formation of southern India. This is interesting in view of the connection of Madagascar with the Indian plate until the mid Cretaceous (Smith et al. 1994). From a simple and highly successful monosulcate prototype, the product of either simultaneous or successive microsporogenesis, two main trends are recognised (Fig. 109). In the rst trend the pollen develop in tetragonal tetrads within the pollen

16 Pollen aperture morphology in Arecaceae mother cell, typical of successive microsporogenesis. Evidence suggests that this is probably the case for all calamoid palms with the possible exception of subtribe Lepidocaryinae. Pollen shape is always symmetric. Within this trend the monosulcate aperture has given rise to equatorially disulcate, extended sulcate, equatorial and sub-equatorialdiporate, incomplete and complete meridional zonosulcate. Although the rst trend is characteristic of calamoid palms, extended sulcate pollen also occur in Licuala (Coryphoideae: Figs. 14, 15) where successive microsporogenesis has been demonstrated (Harley 1999 a) and in some species of arecoid genera: Caryoteae: Arenga; Areceae (Arecinae): Pinanga, Gronophyllum (Fig. 16). Trend 1 In Trend 1 equatorial disulcate pollen are represented by numerous species of calamoid palms. This type of aperture con guration is exclusive to the largest of all palm genera, Calamus, which has at least 360 species, while extended sulcate, equatorial and subequatorial dipory, incomplete and complete zonosulcy are unusual. Disulcy and dipory are exclusive to the calamoid palms, while extended monosulcy and zonosulcy occur in other subfamilies as well. Equatorial disulcate pollen occur in few other monocotyledonous families, for example, Araceae (Grayum 1992), Bromeliaceae (Halbritter 1992), Pontederiaceae (Simpson 1987) and Dioscoreaceae (Caddick et al. 1998). Pollen in these families have been studied without acetolysis, thus it is not easy to compare the results with those for the palms, where the pollen has been acetolysed to allow comparison with fossil pollen. As in palms, both extended and equatorial disulcate pollen occur in Araceae, and Grayum (1992) suggests that extended sulcate is a development of monosulcate leading directly, or indirectly via disulcate, to zonosulcate. A number of genera in Tribe Amaryllideae (Amaryllidaceae) have disulcate pollen, in all cases the exine is gemmate with scattered large spinulae (Schulze 1983, Snijman & Linder 1996). In Bromeliaceae the pollen are per-ellipsoid, and the distal and proximal exine distance between the apertures is considerable in comparison to palms. Disulcate pollen are characteristic of Pontederiaceae, however, the exine topology and (usually appressed baculate elements) and 2-layered ultrastructure with a ``commisural line are particular to Pontederiaceae (Simpson 1987). The fossil record for disulcate pollen is extensive (Ediger 1990). The most frequently recorded genus, Dicolpopollis, is generally considered to represent ancestral calamoid palms. Records are geographically widespread (Table IV ), and include North America, Europe, Malesia, India and Australia. The oldest records with a generally 59 accepted palm-like aynity are from the late Cretaceous (Muller 1968). Outside subfamily Calamoideae equatorial and subequatorial diporate pollen are unknown in Arecaceae. Within Calamoideae the condition occurs in three subtribes of Calameae: Salaccinae (Eleiodoxa), Korthalsiinae(Korthalsia), and Calaminae (Daemonorops). Not all species of Korthalsia have diporate pollen, zonosulcy and equatorial disulcate subtype ``E (where the ``bridges between the two sulci are very fragile and the grains often separate into two halves following acetolysis) are equally common. In those species which do have diporate pollen (Harley 1996) the grains are spheroidal and the two pores are equatorially positioned (Figs. 63± 66). In Daemonorops the pollen shape is ellipsoid and, usually, equatorial disulcate. However, two diporate types occur: equatorial diporate, (Figs. 67, 68), known only for D. oblata J. Dransf., and subequatorial diporate, which has been recorded in D. sparsi ora Becc. (Figs. 69, 72, 74), D. verticillaris (GriYth) Becc. (Figs. 70, 71) and Eleiodoxa (Fig. 73). In Korthalsia and Daemonorops oblata the pollen are intectate and gemmate-spinulose or spiny, while in Eleiodoxa, D. sparsi ora and D. verticillaris the exine is simple tectate. Discrete diporate pollen, readily distinguished from disulcate pollen, are rare in the monocotyledons, there are some examples in Bromeliaceae (Halbritter 1992), although the pores in this family are often very large. In the fossil record Frederiksen et al. (1985) describe a new diporate genus, Diporoconia, with a distribution in North America, Europe and West Africa. Among other taxa, comparison was also made with the subequatorial diporate pollen of Daemonorops. Although the parent plant was probably not an ancestral Daemonorops, they concluded that it was probably monocotyledonous and probably from a palm. However, the granular ultrastructure of the infratectum is not palm-like. Kar (1995) described a new type of aperture ``diporocolpis from the early Eocene of India. Three distinct exine types were apparent and led to the description of three form genera: Piladiporocolpites, Psiladipocolpites and Retidiporocolpites. Although the simple tectate subequatorial pollen of Daemonorops was discussed, no conclusion was made regarding aynity. Proportionately, the pollen wall thickness in Piladiporocolpites and Psiladipocolpites is more comparable with the Daemonorops type than is the wall of Diporoconia. In all the fossil genera, however, the pores are less discrete than in Daemonorops. Like brevi monosulcate pollen the systematic distribution of extended monosulcate pollen is sporadic but widespread. Licuala (Figs. 14, 15) (Coryphoideae), Eugeissona insignis Figs. 40± 50. Aperture type 7. Symmetric trichotomosulcate (sometimes occurs with Aperture type 1); Aperture type 8. Asymmetric trichotomosulcate ( often occurs with Aperture type 2): 40. Acrocomia aculeata (Jacq.) Lodd ex Mart., Hazen 2076, group of grains to show general appearance, type 7 [LMÖ 160]. 41. Bactris concinna Mart., KrukoV 6497, polar view, distal face, type 7 [SEMÖ 2000]. 42. Gastrococos crispa ( Kunth) H.E. Moore, Ekman s.n., two grains, polar views, proximal face right, distal face left, type 7 [SEMÖ 1050]. 43, 44. Hydriastele sp., Millar NGF23072: 43. Symmetric monosulcate grain, polar view, subtype 1A [LMÖ 1000]; 44. Symmetric trichotomosulcate grain, polar view, type 7 [LMÖ 1000]. 45, 46. Reinhardtia simplex (H. Wendl.) Drude & Dammer, Wendland 1857: 45. Asymmetric monosulcate grain, polar view, distal face, subtype 2A [SEMÖ 1650]; 46. Asymmetric trichotomosulcate grain, polar view, distal face, type 8 [SEMÖ 1900]. 47. Chamaedorea brachypoda Standl. & Steyerm., Bailey Hort. 60± 800, two grains, asymmetric trichotomosulcate, left asymmetric monosulcate, subtype 2A [SEMÖ 2000]. 48. Carpoxylon macrospermum H. Wendl. & Drude, Dowe 001, polar view, distal face, type 8 [SEMÖ 2000]. 49, 50. Ceroxylon alpinum Bonpl. Ex D.C., Balslev 62512: 49. Symmetric trichotomosulcate grain, low focus, type 7 [LMÖ 1000]; 50. Asymmetric monosulcate grain, polar view, high-mid focus, subtype 2A [LMÖ 1000].

17 M. M. Harley and W. J. Baker 60 (For legend see page 61). Beccari, E. minor Beccari, E. tristis GriYth (Figs. 17, 18) and E. utilis Beccari, Eremospatha (Fig. 13) (Calamoideae), Arenga, Pinanga ± some, Gronophyllum ± some (Fig. 16) (Arecoideae). Of the extended sulcate fossil pollen, described in the literature, the simple tectate or reticulate Longapertites is the most frequently cited (Table IV ). However, pollen grains assigned to Longapertites sometimes appear to be damaged disulcate pollen (for example, Frederiksen 1994)

18 Pollen aperture morphology in Arecaceae with a broken distal bridge. This is an easy oversight as many fossil disulcate grains have similar exines. Morley (1978) comments that some of the coarsely reticulate species of Longapertites (Frederiksen 1994) show some similarities to Eugeissona. We suggest that the characteristics of the reticulum in these species are very distinct, dupliclavate for example, and may have more in common with pollen of some Asparagalean or Lilialean species or, in the Palms, Ceroxylon (Ceroxyloideae) or perhaps some species of Pinanga (Arecoideae). Jansonius & Hills (1980) comment that in Rao & Ramanujam (1978) the extended sulcate Clavapalmidites hammenii is notably similar in appearance to Paravuripollis mulleri, which is described as zonosulcate. Both genera are recorded in the Miocene of India, and do indeed appear very similar both in size and the apparently extended monosulcate aperture con guration. Quilonipollenites closely resembles the distinctive, thickwalled reticulate pollen of Eugeissona tristis type (Muller 1979). The present distribution of Eugeissona is the Malay Peninsula and Borneo. In India Quilonipollenites is recorded from the Palaeocene (Morley 1998), and from the Miocene (Phadtare & Khulkarni 1984). Thus it is present before and after the Middle Eocene collision of the Indian plate with the Asian plate. From the Middle Eocene Quilonipollenites is reported from Sulawesi and Java (Morley 1998). It is also recorded from the lower Miocene onwards in Borneo (Morley 1977, Muller 1979). Morley (1998) explains the post collision distribution as wholesale dispersal of species from the Indian plate at this time. While the later disappearance of Quilonipollenites (Eugeissona) from India is suggested to be a result of Neogene and Quaternary climatic changes (Morley 1998). Completely zonosulcate apertures in Arecaceae are known only in the Calamoideae (some Salacca and some Korthalsia) and the monotypic subfamily Nypoideae: Nypa fruticans Wurmb. The spiny exine combined with the zonosulcate aperture, and large size (55± 70 mm ± Harley et al. 1991) make the pollen of Nypa highly distinctive. The pollen of Korthalsia that are zonosulcate have a gemmate exine, and show some similarity to Paravuripollis, while the pollen of Salacca are spiny and share a similar ultrastructure to Nypa. However, pollen of Salacca are much smaller (<30 mm) than those of Nypa so distinction is easy. In Salacca and Korthalsia there are some species where the pollen appears to have apparently incomplete zonosulcate apertures, probably a variant of disulcate type 5E. The fossil form genus Spinizonocolpites, which is compared by most authors to the pollen of the recent genus Nypa has a remarkably long and widespread paleogeographic record. Records date with cer- 61 tainty from the Senonian and appear almost simultaneously throughout the palaeotropics. This is in stark contrast with the much more restricted distribution of Nypa fruticans: Malesia, including Sri Lanka, the Ganges Delta, Indochina, northwestern Australia, the Solomon Islands and the Ryukyu Islands ( Uhl & Drans eld 1987). The recent nds from the Eocene of Tasmania (Pole & McPhail 1996) of numerous fossil Nypa fruits in close association with quantities of Spinizonocolpites pollen, add convincing evidence in support of the ancestral relationship between the fossils and the Recent species. Nevertheless, the remarkable invasiveness of these early Nypa-like ancestors that evolved such a unique and extraordinary pollen type is paradoxical. The development of the apertures included in Trend 1 has been subject to discussion. Thanikaimoni (1970) considered that disulcate pollen developed from monosulcate via extended sulcate, with the formation of an exine bridge across the distal pole. In this hypothesis disulcate is not perceived as giving rise to zonosulcate. An alternative hypothesis (Harley 1996, present paper) suggests equatorial disulcate has arisen de novo from monosulcate, and subsequently leads to zonosulcy, via extended sulcate and incomplete zonosulcate. (Fig. 110). The two hypotheses present a more or less circular argument, suggesting that modi cation to the developing aperture template of monosulcate pollen may give rise to interruption of, or to elongation of, the sulcus. Either condition can probably lead subsequently to zonosulcy during the course of evolution. This is supported by the occurrence of extended sulcy in a number of species in the predominantly disulcate calamoid palms, and also in the predominantly monosulcate coryphoid and arecoid palms where disulcy is unknown. Furthermore, incomplete or complete zonosulcate pollen occur in both calamoid and arecoid palms. Trend 2 In the second trend pollen are produced from tetrahedral tetrads. As in Trend 1, the basic aperture type is monosulcate, but gives rise to asymmetric or symmetric trichotomosulcy, incomplete equatorial zonosulcy and apical or subapical tripory. Trichotomosulcatepollen are mostly associated with asymmetric monosulcate pollen. The two forms of sulcus are produced from the same anthers or even tetrads. In subfamilies Ceroxyloideae and Arecoideae there are numerous examples of species producing asymmetric monosulcate and trichotomosulcate pollen (Figs. 45± 47). Less frequently species in subfamily Arecoideae, tribe Cocoeae, produce exclusively trichotomosulcate pollen, for example, subtribe Elaeidinae: Elaeis guineensis Jacq. and subtribe Bactridinae: Figs. 51± 62. Aperture type 9. Symmetric polar monoporate; Aperture type 10. Asymmetric equatorial monoporate: 51± 53. Ravenea albicans (Jum.) Beentje, Perrier de la BaÃthie 11939: 51. Polar view, distal face, subtype 9A [SEMÖ 2500]; 52. Polar view, mid focus, subtype 9A [LMÖ 1000]; 53. Polar view, low focus, subtype 9A [LMÖ 1000]. 54± 56. Areca caliso Becc., Elmer 11898: 54. Polar view, distal face, subtype 9B [SEMÖ 1800]; 55. Polar view, mid focus, subtype 9B [LMÖ 1000]; 56. Polar view, low focus, subtype 9B [LMÖ 1000]. 57. Ravenea madagascariensis Becc., Drans eld JD6430, oblique equatorial view, apertural face, subtype 9A [SEMÖ 3320]. 59± 61. R. sambiranensis Jum. & H. Perrier, Drans eld JD6408: 59. Polar view, mid-low focus, subtype 9A [LMÖ 1000]; 60. Polar view, low focus, subtype 9A [LMÖ 1000]; 61. Equatorial view, note aperture centre top, subtype 9A [LMÖ 1000]. 58, 62. Pogonotium ursinum (Becc.) J. Dransf., Drans eld JD 5877: 58. Polar view, proximal face to show single, sub-equatorially positioned pore, type 10 [SEMÖ 2900]; 62. Group of grains to show single equatorial pores (arrows), various foci, type 10 [LMÖ 1500].

19 M. M. Harley and W. J. Baker 62 Figs. 63± 74. Aperture type 11. Equatorial diporate; Aperture type 12. Sub-equatorial diporate: 63, 64. Korthalsia merrillii Becc., Fernando 638: 63. Equatorial view showing one of the two apertures, subtype 11A [SEMÖ 2360]; 64. Group of grains, to show general appearance (NB. it is almost impossible to see both pores in SEM), subtype 11A [SEMÖ 600]. 65, 66. Korthalsia rigida Blume, GriYth s.n.: 65. Equatorial view, high-mid focus, note aperture interruptions symmetrically positioned on right and left sides of grain, subtype 11A [LMÖ 1000]; 66. Equatorial view, low focus, note aperture interruptions as in ``65, subtype 11A [LMÖ 1000]. 67, 68. Daemonorops oblata J. Dransf., Drans eld et al. JD5712: 67. Equatorial view, high-mid focus, note aperture interruptions symmetrically positioned on right and left sides of grain type 11B [LMÖ 1000]; 68. Equatorial view, low focus, note aperture interruptions as in ``67, subtype 11B [LMÖ 1000]. 69, 72, 74. Daemonorops sparsi ora Becc.: 69. Hose 703, polar view, proximal face, mid-low focus, type 12 [LMÖ 1000]; 72. Keith 4325, equatorial view, long axis, mid-low focus, type 12 [LMÖ 1000]; 74. Tiggi S.3319, polar view, proximal face, type 12 [SEMÖ 2350]. 70, 71. Daemonorops verticillaris (GriYth) Becc., Ridley s.n.: 70. Equatorial view, long axis, mid focus, type 12 [LMÖ 1000]; 71. Polar view, mid-low focus, type 12 [LMÖ 1000]. 73. Eleiodoxa conferta (GriYth) Burret, Whitmore et al. TCW 3104, two grains in oblique equatorial views, proximal faces touching, type 12 [SEMÖ 4500].

20 63 Pollen aperture morphology in Arecaceae Figs. 75± 82. Aperture type 13. Apical triporate; Aperture type 14. Sub-apical triporate. 75, 76. Areca klingkangenesis J. Dransf., Drans eld JD6103: 75. Polar view, type 13 [SEMÖ 1200]; 76. Polar view, high-mid focus, type 13 [LMÖ 1000]. 77± 82. Sclerosperma mannii H. Wendl.: 77, 80± 82. Tuley s.n.: 77. Polar view of two grains touching, proximal faces, possibly still attached from tetrad stage, type 14 [SEMÖ 1200]; 80. Polar view, distal face, high focus, type 14 [LMÖ 1000]; 81. Polar view, proximal face, low focus, same grain as ``80, type 14 [LMÖ 1000]; 82. Polar view, distal face, type 14 [SEMÖ 1750]. 78, 79. Hall & Eriti GC36130: 78. Group of unexpanded grains, convex distal faces with pori visible, type 14 [SEMÖ 1500]; 82. Expanded grain, polar view, distal face, type 14 [SEMÖ 1750]. Acrocomia aculeata (Jacq.) Lodd ex Mart. (Fig. 40), Bactris concinna Mart. (Fig. 41) and Gastrococos crispa ( Kunth) H.E. Moore (Fig. 42). Trichotomosulcate pollen also occur in the order Asparagales (Erdtman 1944; Schulze 1983, Le Thomas et al. 1996, Rudall et al. 1997). The monosulcate ± trichotomosulcate pollen association occurs in some basal dicotyledons, for example Chloranthaceae (Chapman 1987), and therefore would seem to be an important, even key, element in the evolution of the angiosperms. Nevertheless, it is has often

21 M. M. Harley and W. J. Baker 64 (For legend see page 65).

22 Pollen aperture morphology in Arecaceae 65 Figs. 93± 97. Aperture type 17. Inaperturate: Pigafetta elata (Bl.) H.Wendl., Drans eld & Mogea JD3867: 93. Group of grains showing typical collapsed state of pollen, following acetolysis protocols similar to those used for other palm pollen [SEMÖ 1000]; 94. Whole grain, collapsed [SEMÖ 2600]; 95. Whole grain, slight fracture on left [SEMÖ 2600]; 96. Group of grains, high-mid focus [LMÖ 1000]; 97. Group of grains, mid-low focus [LMÖ 1000]. been overlooked or, when asymmetric as it frequently is in the Arecaceae, reported as an abnormality of the monosulcate state (Erdtman 1944). Krutzsch (1970) considered that a form genus (Trichotomosulcites Couper 1953) for ``such atavistic, teratological (fossil) forms, super uous. There are a number of records of dispersed trichotomosulcate and monosulcate pollen, sharing a similar combination of tectum and infratectum, from at least the early mid-cretaceous, for example: Doyle (1973, 1969); GoÂczaÂn & JuhaÂsz (1984); JuhaÂsz & GoÂczaÂn (1985); Walker & Walker (1986); Hughes (1994); Friis et al. (1997). A dicotyledonous origin is widely accepted for most of these oldest dispersed fossil pollen records, although a monocotyledonous source plant cannot always be dismissed without conclusive supporting data. Incomplete zonosulcate pollen are known for a few species of Areca including: A. abdulrahmanii J. Dransf., A. andersonii J. Dransf., and A. chaiana J. Dransf. Similar incomplete zonosulcate to zonosulcate pollen are also found in Araceae (Grayum 1992) but are rare elsewhere. The incomplete zonosulcate pollen of Areca are comparable with the fossil genus Proxapertites. Tri-aperturate pollen are rare in the monocotyledons. They are known in about 14 genera (ten families, and six orders) including the Arecaceae. For example, in: Alismatales [Ruppiaceae: Ruppia L. (Schwanitz 1967)], Liliales [Colchicaceae: Androcymbium Willd. and Merendera Ramond (Schulze 1975); Liliaceae: Tulipa L. ( Kosenko (1990)], Commelinales [Commelinaceae: Tinantia C.B. Figs. 83± 92. Aperture type 15. Incomplete zonosulcate; Aperture type 16. Zonosulcate: 83, 85. Areca abdulrahmanii J. Dransf., Jermy 13707: 83. Unexpanded grain, equatorial view, aperture almost encircling grain from pole to pole, type 15 [SEMÖ 2000]; 85. Polar view, proximal face to show brief tectate ``bridge, connecting the two halves of the grain, type 15 [SEMÖ 2000]. 86, 87. A. andersonii J. Dransf., Anderson S.31937: 86. Unexpanded grain, equatorial view, aperture almost encircling grain from pole to pole, high focus, type 15 [LMÖ 1000]; 87. Description as for ``86, mid focus, type 15 [LMÖ 1000]. 84, 88. A. klingkangensis J. Dransf., George S.42803: 84. Semi expanded grain, aperture membrane intact, aperture almost encircling grain from pole to pole, proximal pole with connecting bridge on right, type 15 [SEMÖ 1600]; 88. Polar view, proximal face, close up of connecting bridge, type 15 [SEMÖ 4800]. 89± 92. Nypa fruticans Wurmb.: 89, 90. Bryan jr. 1277: 89. Zonosulcus vertical to frame, aperture encircles grain from pole to pole, high-mid focus, type 16 [LMÖ 1000]; 90. Description as for ``89, low focus, type 16 [LMÖ 1000]. 91, 92. Whitmore 596: 91. Whole grain, two halves together, aperture encircling the grain from pole to pole [SEMÖ 1200]; 92. Two separated halves of a grain, type 16 [SEMÖ 700].

23 M. M. Harley and W. J. Baker 66 Figs. 98± 107. Tetrad types (pre free microspore stage) in palms: 98, 100, 105. Tetragonal tetrads: 98. Metroxylon vitiense (H. Wendl.) Benth. & J.D. Hooker, Smith 9339 [SEMÖ 2400]; 100. Nypa fruticans Wurmb., Drans eld s.n., mid focus [LMÖ 500]; 105. Model of tetragonal tetrad with disulcate pollen. 99, 101, 106. Tetrahedral tetrads: 99. Chamaedorea pumila H. Wendl. Ex Dammer, N.E. Brown s.n. [SEMÖ 1700]; 101. Dypsis pinnatifrons Mart., Keralidrey 25334, high-mid focus [LMÖ 1000]; 106. Model of tetrahedral tetrad with trichotomosulcate pollen. 102, 107. Decussate tetrads: 102. Licuala ternata GriV. Ex Mart., G. Smith & Sumawong GC77, high focus [LMÖ 900]; 107. Model of decussate tetrad with monosulcate pollen Howea belmooreana (C. Moore & F.v. Mueller) Becc., Moore s.n., polar view, proximal face, to show Y-shaped impression mark [SEMÖ 2280] Daemonorops spectabilis Becc., Chai S.39677, polar view, proximal face, to show linear impression mark [SEMÖ 1350]. Clarke (Rowley & Dahl 1962) and Tradescantia L. (Poole & Hunt 1979); Haemodoraceae: Conostylis R. Br. (Simpson 1983)], and Arecales [Arecaceae: Areca L. and Sclerosperma G. Mann & H. Wendl. (Ferguson & Harley 1993)]. In most of the preceding genera the apertures are sulcate, not porate. There is evidence to suggest that, in Areca, the small, discrete apically positioned pores of Areca klingkangensis J. Dransf. pollen are a chance development from incomplete zonosulcy via trichotomosulcy (Fig. 109, and Harley & Drans eld: in prep.). They are not known elsewhere, the closest comparison is with Conostylis (Haemodoraceae; Zavada 1983), however, the exine topology and strati cation are diverent. In the monocotyledons sub-apically positioned pores are apparently unique to Sclerosperma. In the Arecaceae it is uncertain whether sub-apical tripory has developed via trichotomosulcy or is a discrete state, as no intermediates have been found (Fig. 109). It is signi cant, among the monocotyledons, that triapertury is associated with simultaneous microsporogen-