Dichanthium Willemet is a genus of grasses (family Poaceae, order Poales) comprising roughly 20 species native to the Old World tropics, with centres of diversity in Africa, Asia, and Australia. The genus was established by P. Willemet in 1796 (Ann. Bot. (Usteri) 18: 11).
Plants are typically tufted perennials with stems (culms) that have characteristically bearded nodes. The inflorescence consists of two or more racemes arranged digitately or sub-digitately at the top of the flowering stem. A distinctive feature of the genus is the pairing of spikelets along each raceme: one sessile, bisexual, and awned; the other pedicellate, male or sterile, and awnless. Terminal positions on each raceme bear triplets rather than pairs. Spikelet pairs fall as a unit together with the adjacent rachis joint when mature. The sessile spikelet has a small, shortly bearded callus, a 2-keeled lower glume often furnished with a subapical fringe of hairs, and an upper lemma that tapers into a conspicuous awn.
The genus ranges across the Old World tropics from Africa through South and Southeast Asia to Australia, where 8–10 species occur (5–7 native, 3 naturalized). Several species have also become naturalized in the Americas and on various oceanic islands. The boundaries of Dichanthium have shifted over time: species formerly included here are now placed in the related genera Andropogon, Bothriochloa, Capillipedium, Euclasta, and Pseudodichanthium.
Etymology
The genus name Dichanthium derives from Greek dicha (in two, apart) and anthos (flower), referring to the paired arrangement of spikelets—one sessile and fertile, the other pedicellate and sterile or male—that characterises every raceme. The genus was named by the French botanist P. Willemet in 1796.
Distribution
Dichanthium is native to Old World tropical regions, spanning Africa, South and Southeast Asia, and Australia, where roughly 8–10 species grow across all states (5–7 native, 3 naturalized). Several species—notably D. annulatum and D. aristatum—have been introduced and naturalized in the Americas and on oceanic islands, where they can behave as weeds in disturbed grasslands and pastures.
Ecology
Members of Dichanthium are characteristic plants of open tropical and subtropical grasslands, savannas, and disturbed ground. They are among the dominant grasses of seasonally dry, warm regions. Some species, such as D. annulatum (Angleton grass) and D. aristatum (Harbur grass), are cultivated as pasture and forage grasses valued for palatability and drought tolerance; others are listed as weeds in Australia where introduced populations have spread.
Taxonomy Notes
The circumscription of Dichanthium has contracted since the mid-20th century: species previously included have been transferred to Andropogon, Bothriochloa, Capillipedium, Euclasta, and Pseudodichanthium as generic limits in the Andropogoneae tribe have been refined. The genus was described by P. Willemet (1796) and is placed in the tribe Andropogoneae within the subfamily Panicoideae of the family Poaceae.
