Plants shrub-like, densely clumping; rhizomes pachymorph, the necks less than 25 cm. Culms 2-4 m tall, 0.5-1.5 cm thick, pendulous; nodes prominent; internodes terete, glabrous, smooth or finely ridged. Branches 15--25 per node in the first year, to 80 later, slender, subequal, semi-verticillate, often extravaginal; buds very broadly ovate, with 2 single-keeled bracts, wide open at front with 2 rows of many branch initials visible, open at back. Culm sheaths deciduous, papery, concavely attenuate distally, adaxially scabrous distally; ligule tall, often also adaxially scabrous; blade long, reflexed, subulate. Leaf sheaths deciduous or persistent; blade small to medium-sized, transverse veinlets very obscure. Synflorescence ebracteate, semelauctant, an open, interrupted panicle; branches erect, falcate, usually subtended by a ring of hairs or a very reduced sheath, fasciculate, pulvinae absent. Spikelets with 2 or more fertile florets; glumes delicate, not persistent; lemma ribbed, acute, usually shorter than palea. Stamens 3. Stigmas 2. Name from the Greek, drepanon, ‘sickle’ and stachys, ‘spike’, a reference to the curving branches of the synflorescence.
Drepanostachyum is a genus of about 10 species found along the Himalayas from E Pakistan to SE Tibet and Meghalaya. Many Chinese species originally placed in Drepanostachyum have been transferred to Ampelocalamus. Found under forest types such as oak, these are the most drought-tolerant Sino-Himalayan mountain bamboos. They are also some of the most tender, but dislike humid tropical climates. The species are locally quite variable and boundaries between varieties and species are very difficult to define.
The frequent occurrence of extravaginal branching in this genus and Himalayacalamus is unusual in the woody bamboos and, like the deciduous glumes, may reflect the relatively delicate sheathing throughout.
Distinguished from Himalayacalamus by the falcate, arching panicles of spikelets with 2 or more florets, the scabrous interior surface at the top of the culm sheath and the absence of a larger central branch.
Stapleton, C.M.A. 1994. The bamboos of Nepal and Bhutan Part III: Drepanostachyum, Himalayacalamus, Ampelocalamus, Neomicrocalamus, and Chimonobambusa (Gramineae: Poaceae, Bambusoideae). Edinburgh J. Bot. 51(3): 301--330.