The genus Sorghum Moench is subdivided into sections Chaeotosorghum, Heterosorghum, Parasorghum, Stiposorghum and Sorghum. Section Sorghum includes two rhizomatous species, S. halepense (L.) Pers. (2n = 40) and S. propinquum (Kunth) Hitchcock (2n = 20), as well as the annual S. bicolor (L.) Moench (2n = 20). Sorghum bicolor is divided into subspecies bicolor to include all domesticated grain sorghums, subspecies drummondii (Steud.) de Wet comb. nov. to include stabilized derivatives of hybridization among grain sorghums and their closest wild relatives and subspecies arundinaceum (Desv.) de Wet et Harlan to include the wild progenitors of grain sorghums. Four ecotypes of subspecies arundinaceum are recognized: race aethiopicum of the arid African Sahel, race virgatum of northeastern Africa, race arundinaceum of the African tropical forest, and race verticilliflorum of the African Savanna. The numerous, usually recognized grain sorghums are divided among five basic races, bicolor, caudatum, durra, guinea and kafir, and ten hybrid races that each combine characteristics of at least two of these basic races. Races of grain sorghum are morphologically distinct, and they maintain their unity of type through spacial and ethnological isolation. SORGHUM Moench is a heterogeneous genus. The following sections are usually recognized: Stiposorghum, Parasorghum, Sorghum, Heterosorghum and Chaetosorghum (Garber, 1950). Stiposorghum and Parasorghum are characterized by distinct rings of hairs at each culm node, with the awns of Stiposorghum over 65 mm long and those of Parasorghum substantially shorter. The culm nodes are glabrous or hairy in Sorghum, Chaetosorghum and Heterosorghum, but never do the hairs form a nodal ring. The pedicellate spikelets are reduced to subequal glumes in Heterosorghum and unequal glumes in Chaetosorghum. Section Sorghum is characterized by better developed pedicellate spikelets that are often male fertile but almost always female sterile. Sessile spikelets in the genus Sorghum are