Systematics and biogeography of Senna Mill. (Leguminosae) in the Arabian Peninsula
Aligned DNA sequence data for all accessions analysed for rps16 and matK regions.zip (40.51Kb)
Filimban2013 Figures.pdf (1.105Mb)
Filimban, Faten Zubair Bahnan Bakri
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Senna comprises c.300-350 species and is one of the most species-rich and widely distributed genera in the family Leguminosae (Fabaceae). It is most diverse in tropical America, with secondary centres of diversity in tropical Africa, Madagascar and Australia. Only a few species are found in South Eastern Asia and in the Pacific Islands. Several Senna species are used as purgatives or laxatives in medicine, and some species are cultivated for their attractive flowers and foliage. The taxonomic revision of Senna species from Arabia presented here is based principally on herbarium specimens from the Royal Botanic Garden Edinburgh and the Royal Botanic Gardens, Kew and on field observations made in the Kingdom of Saudi Arabia, the Sultanate of Oman and the Republic of Yemen. These materials and observations also formed the basis for a review of the morphological features of the Senna species in Arabia, which was undertaken in the context of the morphological variability of the whole genus. The taxonomic revision recognises nine species that occur in Arabia: Senna alexandrina Mill., S. didymobotrya (Fresen.) H.S. Irwin & Barneby, S. holosericea (Fresen.) Greuter, S. hookeriana Batka, S. italica Mill., S. obtusifolia (L.) H.S. Irwin & Barneby, S. occidentalis (L.) Link, S. sophera (L.) Roxb. and S. tora (L.) Roxb. The study demonstrated that a putative tenth species, S. socotrana (Serrato) Lock, previously thought to be endemic to the region, is morphologically indistinguishable from the widespread Senna sophera. Consequently the study presents S. socotrana (Serrato) Lock as a syn. nov. Four taxa, S. alata (L.) Roxb., S. artemisioides (DC.) Randell subsp. artemisioides, S. auriculata Roxb., and S. multiglandulosa (Jacq.) H.S. Irwin & Barneby, are recorded as or cultivated in the Arabian Peninsula. A phylogeny is presented for the genus Senna, including all nine Arabian species, based upon the chloroplast DNA regions matK and rps16 and analysed in a parsimony and Bayesian framework. Sampling new to this study included 118 accessions of Arabian species representing substantial parts of their geographic range within the Arabian Peninsula. Sequence data newly generated from a further 13 accessions were added to 104 generated in previous studies bringing the number of accessions representing other Senna species from across the range of the genus to 117. The phylogeny is useful in a taxonomic context and is also suggestive of the phylogenetic utility of some features, especially the morphology of the pods. Reconstruction of the morphological diversification of extrafloral nectaries in the context of the phylogeny suggests that it may have been more complex than outlined in previously published work. The phylogeny shows Senna species found in the Arabian Peninsula are placed in three separate clades, suggesting that Senna arrived in the Arabian Peninsula at least three times independently. Dating the phylogeny using a relaxed molecular clock in a Bayesian approach indicates that these arrivals happened at different times over the past c. 20 Mya, suggesting that a common geological explanation is unlikely and that dispersal must have played a key role in developing these biogeographic patterns.