Systematics of Trigonochloa (Poaceae, Chloridoideae, Chlorideae)

A systematic treatment including descriptions and a key for identification is provided for the two species of Trigonochloa, a genus recently segregated from the polyphyletic Leptochloa s.l. Trigonochloa ranges from southern Africa east to India and Sri Lanka, reflecting the widely ranging T. uniflora. Trigonochloa rupestris has a more limited distribution from East Africa to Yemen. Trigonochloa is diagnosable from other chloridoid grasses based on its unusually flaccid and membranous leaves that have uniquely enlarged lateral cells in the parenchyma sheath surrounding the vascular bundles in T. uniflora (unconfirmed for T. rupestris given limited material), primary and secondary vascular bundles that do not project above or below in fresh material, XyMS+ leaf anatomy, narrow spicate primary inflorescence branches, spikelets with one (or rarely two) florets, thinly membranous to hyaline lemmas, and a trigonous caryopses that bear a narrow but deep sulcus on the hilar side. Lectotypes are designated for Agrostis montana and Cynodon gracilis. The synonym Leptochloa laurentii De Wild. is confirmed for T. uniflora.