Genus: 30 species.
Region: eastern Africa, Arabian Peninsula.
Botany: annual or perennial herbs, rarely shrubs; leaves variable; inflorescences long narrow racemes, with bundles (fascicles) of 1 to 5 flowers,sometimes up to 15; flowers polygamous with five tepals, arranged spirally, fused at the base; stamens 8, joined at the base, with patches of nectar-bearing tissue at the base of the inner whorl; fruit an achene, usually three-angled, often with rows of spinelike structures.