Pollen morphology of trees, shrubs and woody herbs of the coastal plain and the monsoon slopes of Dhofar (Sultanate of Oman)

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1 Webbia 62(2): Pollen morphology of trees, shrubs and woody herbs of the coastal plain and the monsoon slopes of Dhofar (Sultanate of Oman) M. MARIOTTI LIPPI, T. GONNELLI, M. RAFFAELLI. Dipartimento di Biologia Vegetale dell Università Via G. La Pira 4, I Firenze Accettato il 19 Settembre 2007 Morfologia pollinica di alberi, arbusti e erbe perenni della pianura costiera e dei versanti monsonici del Dhofar (Sultanato di Oman) Il presente lavoro è dedicato alla morfologia pollinica delle più comuni piante arboree, arbustive ed erbacee perenni che crescono in Dhofar, nell Oman meridionale. Vengono anche riportate informazioni sull habitus delle piante e sul loro ambiente di crescita. Key word: Dhofar, pollen morphology, Oman, shrubs, trees. Dhofar is a wide region situated in southern Oman, bordering with Yemen and Saudi Arabia. The area is characterised by the presence of a plain which lies along the coast of the Arabian Sea, at the foot of the steep slopes of the escarpment which rise towards the desert plateau of the Arabian peninsula. The coastal plain is interrupted by numerous small estuaries of wadies, which are often separated from the open sea by sand barriers and contain fresh water. The coast and the slopes are influenced by Monsoon regime which causes moistness and rains during summer: the clouds are not able to rise over the escarpment and release precipitations on its slopes. The coastal plain is covered by a semi-desert grassland with scattered small trees and xerophytic shrubs which generally increase towards inland. Wetland vegetation occurs along wadis and estuaries. In eastern Dhofar, woodlands cover the slopes of the escarpment; scattered plants occur on the dry slopes approaching the Yemen border, at west. A Flora of Dhofar was published by Miller and Morris (1988) and many plant groups have been and still are object of investigation. Numerous papers were devoted to the study of Boswellia sacra Flueck., the frankincense tree, a plant economically important for the trade of its resin, from ancient time. B. sacra grows on the arid slopes of western Dhofar, in the mountains near Hasik, and in pre-desert areas at the edge of the Arabian plateau (Thulin & Warfa, 1987; Raffaelli et al., 2003a,b, 2006). An annotated catalogue of the vascular plants of Oman (Ghazanfar, 1992) and a Flora of Oman, including the Flora of Dhofar, is in progress (Ghazanfar, 2003). The pollen morphology of the plants which grow in this area is poorly known. The pollen Flora of Qatar (El- Ghazaly, 1991) is the only exhaustive study in the Arabian Peninsula. However, it includes mainly the species occurring in the plateau and covers only a small part of the plants growing in Dhofar. The only other useful reference palynoflora seems to be that of African savanes (Bonnefille & Riollet, 1980). This statement underlines the affinities between Arabian peninsula and East Africa, from a floristic point of view. However, the pollen morphology of many species is still unstudied. Also paleopalinological investigations carried out in southern Oman are scarce (Lezine et al., 2002; Mariotti Lippi, 2002; Hoorn & Cremaschi, 2004). The aim of this paper is to improve the knowledge of the pollen morphology of the most common trees, shrubs and woody herbs widespread in the coastal plain and the escarpment of Dhofar (Fig. 1). Centro Studi Erbario Tropicale, Università di Firenze - Pubbl. n. 110.

2 246 M. Mariotti Lippi, T. Gonnelli, M. Raffaelli 30 Km Oman Dhofar Thumrayt Mudayy Barbazum Wadi Andur Dahabun Hasik Haluf Wadi Salafab Wadi Halit Ajdarawt Ghadow Salalah Ashanhib W.Darbat Taqah Jibjat Tawi Attayr Khor Rori Mirbat Jabal Samhan 1812 W. Ayn Hilf Sadh Habdin Al Mughsayl Mare Arabico Fig. 1 Dhofar: the grey circles show the localities of plants collection, as reported in Table 1 Materials and Methods Pollen grains were directly collected from plants growing in Dhofar (Table 1). Reference vouchers of the examined species are deposited in the Tropical Herbarium Studies Centre of Florence (FT). The pollen morphology was studied under light microscope (LM) and under scanning electron microscope (SEM). For LM analysis, pollen grains were dehydrated, acetolyzed (Erdtman, 1969) and placed in a 50% water/glycerol solution. For SEM analysis, acetolyzed pollen grains were washed in acetone, dried, and then gold-coated. All the measurements were taken from at least 30 grains per sample, using a LM. For each pollen-type, the subsequent measurements are given: a) length of the polar axis (P) and equatorial axis (E) and their ratio (P/E), or the diameter (D) when the grains were spherical; in some cases two equatorial axes are identified: one larger (Emax) and one smaller (Emin); b) mean diameter of pores and/or mean length of colpi and pseudocolpi; c) mean exine thickness in the middle of the mesocolpium. Other useful parameters are reported, varying from species to species. Terminology is according to Punt et al. (1994). Results ACANTHACEAE Bentia fruticulosa Rolfe - (Plate I, 1-5) Shape: prolate. P/E ratio about 1.6. Outline in polar view: obtuse quadrangular. Dimensions (µm): P E

3 Pollen morphology of trees, shrubs and woody herbs of the coastal plain 247 Table 1 The investigated species: name, site, date of collection and collectors (see also fig. 1). Species site date collectors Acacia nilotica (L.) Willd. Al Mughsayl M.Raffaelli, M.Tardelli, S.Mosti Acacia senegal (L.) Willd. Wadi Darbat M.Raffaelli, M.Tardelli, S.Mosti Acacia tortilis (Forssk.) Hayne between Mirbat and Sadh M.Raffaelli, M.Tardelli, S.Mosti Adenium obesum (Forssk.) Roem. et Schult. pass to Thumrayt M.Mariotti Lippi, T.Gonnelli, G.Lippi Anogeissus dhofarica A.J. Scott Tawi Attayr M.Raffaelli, M.Tardelli, S.Mosti Bentia fruticulosa Rolfe Wadi Darbat M.Mariotti Lippi, T.Gonnelli, G.Lippi Blepharispermum hirtum Oliv. hills near Salalah M.Raffaelli, M.Tardelli, S.Mosti Boscia arabica Pestalozzi Khor Rori M.Mariotti Lippi, T.Gonnelli, G.Lippi Boswellia sacra Flueck. Al Mughsayl M.Mariotti Lippi, T.Gonnelli, G.Lippi Cadaba farinosa Forssk. Khor Rori M.Mariotti Lippi, T.Gonnelli, G.Lippi Capparis cartilaginea Decne. Al Mughsayl M.Mariotti Lippi, T.Gonnelli, G.Lippi Cleome brachycarpa Vahl ex DC. Khor Rori M.Mariotti Lippi, T.Gonnelli, G.Lippi Cleome noeana Boiss. ssp. noeana Wadi Ayn Hilf M.Raffaelli, M.Tardelli, S.Mosti Cassia holosericea Fresen. Taqah M.Mariotti Lippi, T.Gonnelli, G.Lippi Commiphora foliacea Sprague Sadh M.Raffaelli, M.Tardelli, S.Mosti Fagonia luntii Baker Al Mughsayl M.Raffaelli, M.Tardelli, S.Mosti Grewia damine Gaertn. (syn. G. bicolor Juss.) Al Mughsayl M.Raffaelli, M.Tardelli, S. Mosti Jasminum grandiflorum L. ssp. floribundum (Fresen.) P.S. Green Tawi Attayr M.Raffaelli, M.Tardelli, S.Mosti Jatrofa dhofarica A. Radcliffe-Smith Wadi Darbat M.Mariotti Lippi, T.Gonnelli, G.Lippi Justicia diffusa Willd. Wadi Darbat M.Mariotti Lippi, T.Gonnelli, G.Lippi Maytenus dhofarensis Sebsebe Wadi Darbat M.Mariotti Lippi, T.Gonnelli, G.Lippi Ochradenus baccatus Delile Al Mughsayl M.Mariotti Lippi, T.Gonnelli, G.Lippi Olea europaea L. Ghadow M.Raffaelli, M.Tardelli, S.Mosti Plumbago zeylanica L. Tawi Attayr M.Raffaelli, M.Tardelli, S.Mosti Prosopis cineraria (L.) Druce Khor Rori M.Mariotti Lippi, T.Gonnelli, G.Lippi Ruellia patula Jacq. Khor Rori M.Mariotti Lippi, T.Gonnelli, G.Lippi Ruttya fruticosa Lindau Tawi Attayr M.Raffaelli, M.Tardelli, S.Mosti Salvadora persica L. N of Ashanhaib M.Raffaelli, M.Tardelli, S.Mosti Senra incana(cav.) DC. Khor Rori M.Mariotti Lippi, T.Gonnelli, G.Lippi Ziziphus leucodermis (Baker) O. Schwartz Al Mughsayl M.Raffaelli, M.Tardelli, S.Mosti Ziziphus spina-christi (L.) Willd. Al Mughsayl M.Raffaelli, M.Tardelli, S.Mosti

4 248 Pollen class: heterocolpate with 3 colpori and 6 colpi anastomosing in pair at the endings. Some grains (13%) are tetracolporate with 8 colpi. Apertures: anastomosing colpi delimit a small polar triangle, or square. Colpori about 46 µm long; ora lalongate, about 9.5 µm x 7 µm, with a spinulate border and two lateral raised areas of sexine (lips). Exine: tectate perforate suprareticulate homobrochate, about 3 µm thick. Trema area perforated. Plant habit: branched shrub up to 1.5 m tall. Habitat: woodlands on the south slopes of the coastal mountains. Justicia diffusa Willd. - (Plate I, 6-8) Shape: bilateral. The ratio P/Emax is about 1.4; Emax/Emin is about 1.5. Outline in polar view: elliptic. Dimension µm): P Emax Emin Pollen class: dicolporate. Apertures: colpori very narrow, about 24 µm long; ora quite circular to lalongate, about 3.7 µm x 2.3 µm. A little granulate stopple projecting from each pore is present. Exine: Peripheral area (mesocolpium) tectate perforate suprareticulate homobrochate, about 2.3 µm thick in the polar area and 0.7 µm at the equatorial level. Trema area quite rectangular in shape, sometimes showing a slight median constriction, intectate, granulate, usually occupied by two rows (one for side) of 6 insulae, about 2.15 µm in diameter and similar to peripheral area in exine sculpturing; the insulae near the poles are often connected to the peripheral exine. Plant habit: perennial herb. Habitat: dry and open places from the coastal plain to the top of the southern slopes of the mountains. Ruellia patula Jacq. - (Plate I, 9-11) Shape: spheroidal. Dimensions (µm): M. Mariotti Lippi, T. Gonnelli, M. Raffaelli D Pollen class: tri-pentaporate. Apertures: pore subcircular, about 8 µm in diameter. Exine: semitectate reticulate simplicolumellate, homobrochate, about 4.5 µm thick; lumina about 9 µm wide with wavy outline and numerous short pila in the meshes. Plant habit: perennial herb. Habitat: wadi beds and dry areas. Ruttya fruticosa Lindau - (Plate I, 12-14) Shape: spheroidal to subprolate-spheroidal. P/E ratio about 1.1. Outline in equatorial view: circular or elliptic. Dimensions (µm): P E Pollen class: heterocolpate with 3 colpori and 6 colpi. Apertures: colpori µm long, longer than colpi; colpus membrane scabrate. Ora circular, about 10 µm in diameter, or slightly lalongate. Exine: semitectata, microreticulata, about 2.5 µm thick. Plant habit: shrub or small tree up to 3 m tall. Habitat: woodlands on the southern slopes of the coastal mountains NOTE: pollen grains of Acanthaceae, particularly Bentia, Justicia and Ruellia, appreciably decrease in size during the preparation for SEM analysis. APOCYNACEAE Adenium obesum (Forssk.) Roem. et Schult. - (Plate I, 15-17) Shape: oblate spheroidal. P/E ratio about 0.9. Outline in polar view: spheroidal. Outline in equatorial view: subspheroidal. Dimensions (µm): P E

5 Pollen morphology of trees, shrubs and woody herbs of the coastal plain 249 Pollen class: tetraporate or triporate. Apertures: 4, sometimes 3, well defined pores about 5 µm in diameter, irregularly spaced, surrounded by a thin smooth annulus. Exine: tectate, about 2.5 µm in thickness. Tectum imperforate, slightly scabrate, standing on columellae which are ramified at the distal end. Plant habit: succulent shrub or tree m tall. Habitat: dry places, from the coastal plain to the southern slopes of the mountains, to the northern predesertic area. BURSERACEAE Boswellia sacra Flueck. - (Plate I, 18-21) Shape: subprolate. P/E ratio about 1.2. Outline in polar view: circular to triangular. Dimensions (µm): P E Apertures: colpori about 40 µm long, tapering at both the ends, with costae thickened at the equator; colpus membrane scabrate. Ora circular, about 5.5 µm in diameter. Exine: tectate perforate, µm in thickness; perforations less than 1 µm wide, irregularly distributed. Plant habit: tree up to 6-7 m tall, commonly branched from the base, rarely with a single trunk. Habitat: north pre-desertic area behind the coastal mountains, but also on the hills and the mountainous slopes facing the Indian Ocean. Commiphora foliacea Sprague - (Plate I, 22-24) Shape: spheroidal. Dimensions (µm): D Apertures: short colpori protruding, 8-10 µm long. Ora circular, about 4 µm in diameter. Exine: semitectate reticulate, simplicolumellate, homobrochate, microechinate, about 2 µm thick. Reticulum continuous all over the surface; lumina non homogeneous. Very sharp microspines aligned on the mura. Plant habit: dioecious shrub, non-spiny, many branched, up to m tall. Habitat: hilly and mountainous drier areas. CAPPARACEAE Boscia arabica Pestalozzi - (Plate I, 25-27) Shape: subprolate. P/E ratio about 1.2. Outline in polar view: triangular. Dimensions (µm): P E Apertures: colpori about 21 µm long, parallel or slightly tapering at the ends, with smooth colpus membrane. Ora lalongate or circular, in this case about 4.5 µm in diameter. Exine: tectate, perforate, microechinate, about 4 µm thick in the mesocolpia. Columellae distinct, tightly close together, simple or digitate, longer in the mesocolpia and at the poles. Microspine stout, irregularly spaced. Plant habit: evergreen tree up to 5-6 m tall. Habitat: hills at the base of southern slopes of the coastal mountains. Cadaba farinosa Forssk. - (Plate II, 1-5) Pollen shape: subprolate to prolate. Mean P/E ratio 1.3. Outline in polar view: trilobate. P E Apertures: colpori about 22 µm long, tapering at the ends, with smooth colpus membrane. Ora with illdefined limit, about 4 µm wide, covered by scabrous ectexine elements. Exine: tectate perforate, microechinate, about 2 µm thick. Columellae simple or, rarely, digitate, different in diameter. Microspines irregularly spaced, often with hooked apex, some 1 µm long.

6 250 M. Mariotti Lippi, T. Gonnelli, M. Raffaelli Plate I Fig. 1-5 Bentia fruticulosa: 1. SEM, equatorial view; 2. SEM, polar view; 3. SEM, detail of the exine; 4. LM, equatorial view, high focus; 5. LM, equatorial view, optical cross-section. Fig. 6-8 Justicia diffusa: 6. SEM, equatorial view showing trema area; 7. SEM, equatorial view; 8. LM, equatorial view, optical cross-section. Fig Ruellia patula: 9. LM, high focus ; 10. SEM ; 11, SEM detail of the exine. Fig Ruttya fruticosa: 12. SEM; 13. LM, equatorial view; 14. LM, polar view. Fig Adenium obesum: 15. SEM; 16. LM, optical cross-section; 17. LM, high focus. Fig Boswellia sacra: 18. SEM, equatorial view; 19. SEM, polar view; 20. LM, polar view; 21. LM, equatorial view. Fig Commiphora foliacea: 22. SEM, polar view; 23. LM, polar view; 24. equatorial view. Fig Boscia arabica: 25. SEM, equatorial view; 26. LM, polar view; 27. LM, equatorial view.

7 Pollen morphology of trees, shrubs and woody herbs of the coastal plain 251 Plant habit: shrub up to 2 m tall. Habitat: drier areas, on rocky slopes, gravel plains and open woodlands. Capparis cartilaginea Decne. - (Plate II, 6-10) Pollen shape: subprolate. P/E ratio Outline in polar view: trilobate. P E Apertures: colpori geniculata converging at the poles, about 14 µm long; colpus membrane smooth. Ora circular, protruding from colpi, covered by ectexine granules. Exine: tectate with indistinct, minute perforations, about 1.5 µm in thickness. Sexine surface scattered with minute, faint microspines with a large basis. Plant habit: evergreen spiny shrub, climbing and often hanging from cliffs. Habitat: drier areas on cliffs and rocky places. Cleome brachycarpa Vahl ex DC. (Plate II, 11-14) Pollen shape: spheroidal. D Apertures: colpori about 11 µm long, with uneven margins; colpus membrane granulate. Ora inconspicuous, often not discernible due to overlying granules. Exine: tectate perforate microverrucate, µm in thickness. Sexine slightly thicker than nexine. Plant habit: perennial herb, cm tall. Habitat: drier areas, common in the wadi beds. Cleome noeana Boiss. ssp. noeana - (Plate II, 15-19) Pollen shape: subprolate. P/E ratio about 1.2. Outline in equatoril view: elliptic. P E Pollen class : tricolporate. Apertures: colpori about 22.5 µm long, tapering at the ends, the middle portion occupied by scabrous ectexine elements which cover the ora. Exine: tectate perforate suprareticulate, about 2 µm thick. Reticulum heterobrochate, simplicolumellate, with circular-elongate lumina. Longitudinal muri generally more pronounced than the transversal ones. Perforations 1-3 per lumen. Plant habit: perennating or perennial herb or small shrub, cm tall. Habitat: stony wadi beds. CELASTRACEAE Maytenus dhofarensis Sebsebe - (Plate II, 20-24) Pollen shape: spheroidal to subprolate. Mean P/E ratio 1.1. Outline in equatorial view: subcircular. P E Apertures: colpi well distinct, tapering at the ends, about 18 µm long, apparently interrupted at the equator; colpus membrane scabrous, covered by microgranules. Ora lalongate to subcircular, about 3.5 µm wide, protruding. Exine: semitectate reticulate, simplicolumellate, heterobrochate. Lumina irregular in shape, generally more than 1 µm large, abruptly decreasing in size towards the colpi edges. Plant habit: spiny shrub or small tree, 2-3 m tall. Habitat: woodlands on the south costal mountains and dry plateaux. COMBRETACEAE Anogeissus dhofarica A.J. Scott - (Plate II, 25-29) Pollen shape: subprolate. P/E ratio about Outline in polar view: oval. Outline in equatorial view: esalobate.

8 252 M. Mariotti Lippi, T. Gonnelli, M. Raffaelli Plate II Fig. 1-5 Cadaba farinosa: 1. SEM, equatorial view; 2. SEM, detail of the exine; 3. LM, polar view; 4. LM, equatorial view, optical cross-section; 5. LM, equatorial view, high focus. Fig Capparis cartilaginea: 6. SEM, equatorial view; 7. SEM, polar view; 8, LM, polar view; 9. LM, equatorial view, high focus; 10. LM, equatorial view, optical cross-section. Fig Cleome brachycarpa: 11. SEM, equatorial view; 12. LM, equatorial view, high focus; 13. LM, equatorial view, optical cross-section; 14. LM, polar view. Fig Cleome noeana: 15. SEM, equatorial view; 16. SEM, polar view; 17. LM, equatorial view, high focus; 18. LM, equatorial view, optical cross-section; 19. LM, polar view. Fig Maytenus dhofarensis: 20. SEM, equatorial view; 21. SEM, polar view; 22. LM, equatorial mesocolpial view; 23. LM, equatorial apertural view; 24. LM, polar view. Fig Anogeissus dhofarica: 25. LM, equatorial view; 26. LM, polar view; 27, 28. SEM, equatorial view; 29. SEM, quite polar view.

9 Pollen morphology of trees, shrubs and woody herbs of the coastal plain 253 P E Pollen class: heterocolpate with 3 colpores and 3 colpi. Apertures: colpori about 13 µm long, with granulate colpus membrane. Ora circular or approximately squared, sometimes slightly rectangular. Colpi shorter than colpori, about 11 µm long, with granulate colpus membrane. Exine: tectate, about 4 µm thick. Tectum imperforatum, covered by almost regularly scattered acute microspines, sometimes transversally coalescent, and forming transversal short crestae. Plant habit: deciduous tree up to 12 m tall. Habitat: common tree forming luxuriant woods on the south slopes of the monsoon coastal mountains. COMPOSITAE Blepharispermum hirtum Oliv. - (Plate III, 1-5) Pollen shape: spheroidal to subprolate. Outline in equatorial view: circular to subcircular. Dimension including spines (µm): P 36, E 33 22, Apertures: colpori tapering at the ends, about 22 µm long; colpus membrane granulate. Ora distinct, circular, less than 2 µm in diameter. Exine: tectate perforate echinate, 7-8 µm in thickness including spinae, these last about 5 µm long, smooth, broad at the bases and gradually tapering towards the apices. Plant habit: deciduous shrub or small tree, m tall. Habitat: woodlands on the foothills and south slopes of the coastal mountains. EUPHORBIACEAE Jatrofa dhofarica A. Radcliffe-Smith - (Plate III, 6-9) Pollen shape: spheroidal. D Pollen class: inaperturate. Exine: retipilate, about 4.5 µm thick. Pila with short columellae, less than 1 µm high, and very swollen capita, longitudinally costate, tightly close together. The capita appear subsphaerical in transversal section, about 2 µm in diameter, and quite triangular in tangential view, due to the contiguity with the adjacent ones. Plant habit: deciduous shrub, 1-3 m tall. Habitat: coastal plain, foothills, south mountainous slopes in dry habitats and woodland clearings. LEGUMINOSAE Cassia holosericea Fresen. - (Plate III, 10-15) Pollen shape: spheroidal to subprolate. Outline in polar view: triangular. Outline in equatorial view: oval. P E Apertures: colpori geniculate, equatorially costricted, about 27 µm long, with smooth margines particularly developed at the equator, covering the ora; apocolpial field very small; colpus membrane smooth. Ora circular, about 4 µm large. Exine: tectate perforate, scabrate-rugulate, about 2.5 µm thick. Plant habit: perennial herb or shrub, m tall. Habitat: Coastal plain and sandy depression in the pre-desert and desert areas. Acacia nilotica (L.) Willd. - (Plate III, 16-18) Pollen shape: 16-celled bicovex disc. Dimension of the whole polyad (µm): Main diameter Minor diameter Thickness Pollen class: polyad. Monads: central cell with squared outline, 3 syncolporate, with pores circular with a thin annulus; pe-

10 Plate III Fig. 1-5 Blepharispermum hirtum: 1. SEM, equatorial view; 2. SEM, polar view; 3. LM, equatorial view, high focus; 4. LM, equatorial view, optical cross-section; 5. LM, polar view. Fig. 6-9 Jatrofa dhofarica: 6. LM; 7. LM, detail of the exine; 8. SEM, detail of the exine; 9. SEM, cross section of the exinic wall. Fig Cassia holosericea: 10. SEM, equatorial view; 11. SEM, polar view; 12, SEM, detail of the exine; 13. LM, equatorial mesocolpial view; 14. LM, equatorial apertural view; 15. LM, polar view. Fig Acacia nilotica: 16. SEM, polyad, main diameter; 17. LM, polyad, main diameter; 18. LM, polyad, minor diameter. Fig Acacia senegal: 19. SEM, polyad, main diameter; 20. LM, polyad, main diameter; 21. LM, polyad, minor diameter. Fig Acacia tortilis: 22. SEM, polyad, main diameter; 23. LM, polyad, main diameter; 24. LM, polyad, minor diameter. Fig Prosopis cineraria: 25. SEM, equatorial view; 26. SEM, polar view; 27. LM, equatorial mesocolpial view; 28. LM, equatorial apertural view; 29. LM, polar view.

11 Pollen morphology of trees, shrubs and woody herbs of the coastal plain 255 ripheral cell square to rectangular in outline, 4 syncolporate, colpi H-shaped. Exine: tectate perforate, foveolate, about 2.5 µm thick. Few perforations approximately circular, irregularly spaced. Plant habit: tree to 5 m tall. Spines strong and straight. Habitat: at the base of the southern slopes of the coastal chain, especially in wet places. Acacia senegal (L.) Willd. - (Plate III, 19-21) Pollen shape: 16-celled biconvex disc. Dimension of the whole polyad (µm): Main diameter Minor diameter Thickness Pollen class: polyad. Monads: central cell with almost squared outline, 8 porate; peripheral cell more or less rectangular in outline, 8 porate. Exine: tectate perforate, smooth, about 2.5 µm thick. Perforations approximately circular, different in diameter, closely spaced in shallow depressions. Plant habit: tree or rarely shrub, 6 m tall. Spines in threes at the nodes. Habitat: dry lower southern slopes of coastal chain. Acacia tortilis (Forssk.) Hayne - (Plate III, 22-24) Pollen shape: 16-celled bicovex disc. Dimension of the whole polyad (µm): Main diameter Minor diameter Thickness Pollen class: polyad. Monads: central cell with tetrangular outline, 3 syncolporate; peripheral cell square to rectangular in outline, 4 syncolporate, colpi H-shaped. Exine: tectate perforate, smooth, about 2 µm thick. Perforations closely spaced in shallow irregularly shaped depressions. Plant habit: tree up to 4 m tall. Spines in pairs at the nodes. Habitat: drier places on the coastal hills and drier northern areas behind the mountains. Prosopis cineraria (L.) Druce - (Plate III, 25-29) Pollen shape: subprolate-spheroidal. P E Apertures: colpori tapering at the ends, with almost smooth colpus membrane, about 27 µm long; apocolpial field small; ora distinctly circular, with a thin annulus, about 4 µm in diameter. Exine: tectate perforate, smooth or lightly rugulate, about 2.5 µm thick. Plant habit: tree up to 12 m tall. Habitat: synanthropic in many places of Dhofar MALVACEAE Senra incana (Cav.) DC. - (Plate IV, 1-3) Pollen shape: spheroidal. D D without spines Pollen class: periporate. Apertures: pores approximately circular, about 5.5 µm in diameter, operculate, regularly spaced at about 18 µm each from the other. Operculum persistent, with a sculpturing different from the surrounding surface. Exine: tectate perforate echinate. Perforations minute, closely spaced. Spinae smooth, conical, with blunt apices, regularly spaced. Tectum covered by irregularly spaced microgranules. Columellae longer at the spine bases, swollen in the middle. Plant habit: perennial herb or small shrub, 0,5-1 m tall. Habitat: sandy places of the coastal plain as well as in the wadi beds of drier areas. OLEACEAE Jasminum grandiflorum L. ssp. floribundum (Fresen.) P.S. Green - (Plate IV, 4-7) Pollen shape: spheroidal.

12 256 D Apertures: colpori very narrow, about 31.5 µm long. Ora distinctly circular, about 2 µm in diameter. Exine: semitectate reticulate, simplibaculatae, heterobrochate, about 4.5 µm thick. Lumina irregular in shape, main axis measuring 1-4 µm. Muri with smooth tangential surface. Plant habit: trailing or scrambling perennial herb or shrub up to 3 m tall. Habitat: over trees and shubs in the woodlands of the southern slopes of the monsoon coastal mountains. Olea europaea L. - (Plate IV, 8-12) Pollen shape: spheroidal. D Apertures: colpori very narrow, about 13.5 µm long. Ora circular. Exine: semitectate reticulate, microechinate, about 2.5 µm thick. Reticulum simplicolumellate, heterobrochate. Lumina very irregular in shape, main axis measuring 1-3 µm. Muri with a row of microspine on the tangential surface. Plant habit: evergreen tree, 2-10 m tall. Habitat: woodlands of the coastal mountains. PLUMBAGINACEAE Plumbago zeylanica L. - (Plate IV, 13-17) Pollen shape: spherical. Outline in polar view: circular to lobate. D Pollen class: tricolpate; some grains syncolpate. Apertures: colpi tapering at the ends, about 44.5 M. Mariotti Lippi, T. Gonnelli, M. Raffaelli µm long, sometimes confluent with the adjacent ones (syncolpate grains). Exine: tectate echinate, about 4.5 µm thick. The exine presents: a thin foot-layer, a layer of columellae, an indistinct/ill-defined tectum, a layer of spines slightly longer than the underneath columellae, swollen at the distal end, with acute apex. The spines are irregularly scattered, single or in clusters of 2-6 units. Some spines are digitate. Plant habit: scrambling perennial herb or shrub, 1-2 m tall. Habitat: southern slopes of the coastal mountains in wet places. RESEDACEAE Ochradenus baccatus Delile - (Plate IV, 18-22) Pollen shape: subprolate. P/E ratio about 1.1. Outline in polar view: circular to lobate. P E Apertures: colpori narrow, about 19 µm long; colpus membrane granular. Ora indistinct. Exine: semitectate reticulate, simplicolumellate, heterobrochate. Lumina circular or irregular in shape, decreasing in size towards the poles. Plant habit: dioecious shrub up to m tall. Habitat: drier areas, in coastal plain, hills and mountainous slopes. RHAMNACEAE Ziziphus leucodermis (Baker) O. Schwartz - (Plate V, 1-6) Pollen shape: suboblate to spheroidal. P/E ratio ranging from 0.8 to 1. Outline in polar view: triangular. Outline in equatorial view: circular-irregularly elliptic. P E Apertures: colpori narrow, with thickened costae particularly near the ora, about 22 µm long; colpus

13 Pollen morphology of trees, shrubs and woody herbs of the coastal plain 257 Plate IV Fig. 1-3 Senra incana: 1. SEM; 2. LM, optical cross-section; 3. LM, high focus. Fig. 4-7 Jasminum grandiflorum L. ssp. floribundum : 4. SEM, equatorial view; 5. SEM, polar view; 6. LM, equatorial view; 7. LM, polar view. Fig Olea europaea: 8. SEM, equatorial view; 8. SEM, polar view; 10. SEM, detail of the exine; 11. LM, equatorial view; 12. LM, polar view. Fig Plumbago zeylanica: 13. SEM, equatorial view; 14. SEM, polar view; 15. SEM, cross-section of the exinic wall; 16. LM, equatorial view; 17. LM, polar view. Fig Ochradenus baccatus: 18. SEM, equatorial view; 19. SEM, polar view; 20. LM, equatorial view, high focus; 21, LM, equatorial view, optical cross-section; 22. LM, polar view.

14 258 membrane granulate. Ora circular, about 1.8 µm in diameter, often not exactly located on the equatorial plane. Exine: rugulate-striate, less than 2 µm thick. Mura short, variously oriented, interwoven in the mesocolpia; longer and quite parallel near the poles. Plant habit: intricately spiny shrub to 2 m tall, with zig-zaging branches. Habitat: dry places and desert areas. Ziziphus spina-christi (L.) Willd. - (Plate V, 7-12) Pollen shape: suboblate to spheroidal. P/E ratio ranging from 0.85 to 1. Outline in polar view: triangular. Outline in equatorial view: circular-irregularly elliptic. P E Apertures: colpori narrow, with thickened costae particularly near the ora, about 23 µm long; colpus membrane granulated. Ora circular, less than 2 µm in diameter, often not exactly located on the equatorial plane. Exine: rugulate, about 2.5 µm thick, with very short interwoven mura; almost smooth at the poles and along the colpore margines. Plant habit: tree to 12 m tall or shrub with zigzagging branches. Habitat: coastal plain, hills and mountains, naturalised and also cultivated. SALVADORACEAE Salvadora persica L. - (Plate V, 13-16) Pollen shape: subprolate to prolate. P/E ratio from 1.2 to 1.4. Outline in polar view: lobate. P E Pollen class: tricolporate or tricolpate. Apertures: colpori about 16 µ long, with almost parallel edges, constricted at the equator; colpus membrane smooth. Ora ill-defined. M. Mariotti Lippi, T. Gonnelli, M. Raffaelli Exine: tectate perforate, about 1.5 µm thick. Perforations minute, circular, different in size, homogeneously scattered. Plant habit: evergreen shrub or small tree up to 2-3 m tall. Habitat: coastal plain, drier places, wadi banks. TILIACEAE Grewia damine Gaertn. (Syn.: G. bicolor Juss.) - (Plate V, 17-19) Pollen shape: prolate. Outline in polar view: circular to slightly lobate. P E Apertures: colpori slit-shaped, about 65 µm long; colpi costae along the sides, abruptly thickened towards the equator where they are interrupted; colpus membrane smooth, with few isolate ectexine elements, scabrous at the equator. Ora lalongate, often with indistinct edges, about 11 µm long. Exine: tectate perforate, suprareticulata, simplicolumellate, about 3 µm thick; reticulum continuous all over the surface, with lumina irregular in shape, angular, sometimes longitudinally or obliquely elongated at the equator, ranging from 2 to 4 µm in wide; perforations distinct. Plant habit: shrub or small tree, 2-3 m tall. Habitat: monsoon mountains and dry areas touched by the monsoon moisture. ZYGOPHYLLACEAE Fagonia luntii Baker - (Plate V, 20-22) Pollen shape: subprolate. P/E ratio about 1.1. Outline in polar view: trilobate. P E Apertures: colpori geniculate, about 19 µm long, slightly constricted at the equator; colpus membrane smooth. Ora often not easily discernible, lalongate.

15 Pollen morphology of trees, shrubs and woody herbs of the coastal plain 259 Plate V Fig. 1-6 Ziziphus leucodermis: 1. SEM, polar view; 2, SEM, particular of the exine at the pole; 3. SEM, detail of the exine; 4. LM, equatorial view, optical cross-section; 5. LM, equatorial view, high focus; 6. LM, polar view. Fig Ziziphus spina-christi: 7. SEM, equatorial view; 8, SEM, polar view; 9. SEM, detail of the exine; 10. LM, equatorial view, optical cross-section; 11. LM, equatorial view, high focus; 12. LM, polar view. Fig Salvadora persica: 13. SEM, equatorial view; 14. SEM, polar view; 15. LM, equatorial view; 16. LM, polar view. Fig Grewia damine: 17. SEM, equatorial view; 18. SEM, detail of the exine; 19. LM, equatorial view. Fig Fagonia luntii: 20. SEM, equatorial view; 21. LM, equatorial view; 22. LM, polar view. Exine: tectate microreticulate, about 2.5 µm thick. Lumina oval to irregular in shape, abruptly decreasing in shape towards the colpi. Plant habit: unarmed perennial herb or small shrub with orbicular leaves, up to m tall. Habitat: hills and wadi beds. Acknowledgments We wish to thank the Adviser for Cultural Affairs, Sultanate of Oman, for the logistic assistance during our visit to Dhofar. We also thank Gilberto Montuori e Patrizio Nuti for the technical assistance and Dr. Cristina Bellini for the revision of the language.

16 260 M. Mariotti Lippi, T. Gonnelli, M. Raffaelli REFERENCES BONEFILLE R., RIOLLET G., Pollens des savanes d Afrique orientale. CNRS, Paris. EL-GHAZALY G.A., Pollen Flora of Qatar. Scientific Applied Research Centre, Doha. GHAZANFAR S.A., An annotated catalogue of the vascular plants of Oman. Scripta Botanica Belgica 2. GHAZANFAR S.A., Flora of the Sultanate of Oman. 1. Meise, National Botanic Garden. HOORN C., CREMASCHI M., Late Holocene palaeoenvironmental history of Khawr Rawri and Khawr Al Balid (Dhofar, Sultanate of Oman). Palaeogeography, Palaeoclimatology, Palaeoecology 213: LÈZINE A-M., SALIÈGE J-F., MATHIEU R., TAGLIATELA T-L., MERY S., CHARPENTIER V., CLEUZIOU S., Mangroves of Oman during the late Holocene: climatic implications and impact on human settlements. Veget. Hist. Archaeobot. 11: MARIOTTI LIPPI M., Indagini palinologiche nel sito archeologico di Sumhuram (Khor Rori) in Dhofar (Oman). Primi risultati. Egitto e Vicino Oriente 25: MILLER A.G., MORRIS M., Plants of Dhofar. The Office of the Adviser for Conservation of the Environment, Diwan of Royal Court, Sultanate of Oman. Holmes McDougal Limited Edinburg, Scotland. PUNT W., BLACKMORE S., NILSSON S., LE THOMAS A., Glossary of pollen and spore terminology. LPP Contributions series n 1., LPP Foundation, Utrecht. RAFFAELLI M., TARDELLI M., MOSTI S., The frankincense Tree (Boswellia sacra Flueck., Burseraceae) in Dhofar, Southern Oman: field-investigations on the natural populations. Webbia 58(1): RAFFAELLI M., MOSTI S., TARDELLI M., Boswellia sacra Flueck. (Burseraceae) in the Hasik area (eastern Dhofar, Oman) and the list of the surrounding flora. Webbia 61 (2): THULIN M., WARFA A.M., The frankincense trees (Boswellia ssp., Burseraceae) of Northern Somalia and Southern Arabia. Kew Bull. 42 (3): Summary: This paper describes the pollen morphology of the most common trees, shrubs and woody herbs growing in the coastal plain and the escarpment of Dhofar, a wide region in southern Oman. The plant habit and habitat are also reported.