The Phareae and Streptogyneae (Poaceae) of Sri Lanka : a morphological-anatomical study / Thomas R. Soderstrom, Roger P. Ellis, and Emmet J. Judziewicz

A morphological-anatomical study of the herbaceous bamboos (Poaceae: Bambusoideae) of Sri Lanka is presented. The occurrence of Scrotochloa urceolata and Leptaspis zeylanica of the Phareae and Streptogyna crinita of the Streptogyneae on the island represents the easternmost region in which these tribes of animal-dispersed, rain forest grasses are found together, a fact of phytogeographic significance, since both groups are the only herbaceous bamboo tribes found in both the Old World and the New World. Morphologically, Leptaspis and Scrotochloa possess strongly pseudopetiolate, inverted, obliquely-veined, usually broad leaves with an inner ligule and transverse veinlets. The inflorescence is an open panicle bearing unisexual, one-flowered spikelets; the mature female florets are inflated and covered with uncinate macrohairs that facilitate epizoochory, and the male spikelets have six stamens. Streptogyna has narrower, non-inverted, parallel-veined leaves that possess inner and outer ligules. The perfect, several-flowered spikelets have two or three stigmas and two stamens and are borne in a spikelike raceme; at maturity the florets may detach and adhere to animals by means of a complex of awns, retrorsely barbed stigmas, and rachilla internodes. Details of leaf anatomy indicate that both tribes are peripheral members of the Bambusoideae.Transverse sections of the blades reveal typically bambusoid features such as a complex midrib vasculature, prominent fusoid cells, at least rudimentary arm cells, a multi-layered inner vascular bundle sheath composed of small, thick-walled cells, and an outer bundle sheath of large, colorless cells. The epidermides of the Phareae and Streptogyneae are quite distinct from each other and from typical bamboos. The pharoid grasses, unlike bamboos, possess intercostal fibrous bands, dumbbell-shaped, horizontal silica bodies, and poorly developed bulliform cells. Streptogyna, while less anomalous, also possesses somewhat fiber-like intercostal cells. Bicellular microhairs and well-developed, minute epidermal papillae, both typically bambusoid features, are absent from the leaf-blades of both tribes.