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Genus Dicoma in Tribe Dicomeae

In botanical taxonomy, a genus (plural genera) is a rank used to group closely related species within a family. In the hierarchy, genus sits below family and above species.

Genera are defined by shared morphological, anatomical, and genetic characteristics (for example, features of flowers, fruits, seeds, or leaves) that indicate a close evolutionary relationship among the species they contain.

Each genus can include one or more species. Examples include Rosa (roses) and Solanum (nightshades, including tomato and eggplant).

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Genus Description

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Dicoma, as circumscribed in modern floristic works, belongs to the Asteraceae tribe Dicomeae, distinct within the tribe by achenes bearing a pappus of well-defined scales often flanked by one to several long bristles per achene (Pope, 1992;bentham, 1873). About 50–55 species occur across sub-Saharan Africa, Madagascar, the Arabian Peninsula and western India, with centers of diversity in southern Africa and the Somali–Masai region; the type species is Dicoma capensis (L.) Druce (Pope, 1992; wills et al., 2007). Most species are perennial herbs or subshrubs, with some annuals, typically having entire to shallowly toothed leaves, often with dense indumentum of star-shaped hairs; capitula are solitary or few per stem, with pappus-bearing achenes that are usually obovoid to subcylindric (Pope, 1992; bentham, 1873). Southern African taxa dominate in open woodland, karoo and grasslands, often on shallow soils over rock or calcareous substrates; Malagasy and Indian Ocean island taxa occur in littoral, limestone outcrop and dry forest habitats from sea level to c. 1500 m (Pope, 1992; masinde & harley, 1999). Pollination is predominantly entomophilous, as in most Asteraceae, with capitula usually radiate; fruit are cypselae dispersed by wind via the scale-and-bristle pappus, and secondarily by animals (Pope, 1992; wills et al., 2007). Base chromosome number x=9 has been reported for southern African taxa (2n=36), indicating polyploid series; other counts are sparsely documented (Pope, 1992; wills et al., 2007). No stable subgeneric scheme has gained consensus; historical sectional treatments (Dicoma sensu stricto vs. sect. Pseudo-nardus with persistent outer capitular bracts) are variably applied (bentham, 1873; pope, 1992). Recent floristic treatments accept narrow endemics (e.g., D. reticulata) and recognize several species long maintained under earlier synonyms (pope, 1992; wfo, 2024). Human relevance is modest: several species are ornamental in xeriscapes and rock gardens; a few are browsed or weedy on degraded rangelands (pope, 1992; wills et al., 2007). Conservation concerns focus on habitat loss and overgrazing; targeted surveys and phylogenetic resolution of tropical East African taxa remain research priorities (powo, 2024; masinde & harley, 1999).

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