Dichanthelium is a genus of approximately 72 species of perennial grasses in the family Poaceae, commonly called rosette grasses or panicgrasses. The genus was formerly treated as a subgenus of the large, heterogeneous genus Panicum and was raised to full genus rank in 1974; molecular evidence supports its recognition as distinct, though some taxonomic authorities still include its species within Panicum.
The plants are perennial, occasionally producing short rhizomes. A distinctive feature of the genus is a biphasic growth habit: many species overwinter as basal rosettes of short, broad leaves, then send up taller stems bearing progressively longer and narrower leaves in spring. Stems are hollow and range from a few centimetres to well over one metre in height. The upper stems branch into open panicles. The genus produces two kinds of panicles: primary panicles that may be open-pollinated (chasmogamous), and smaller secondary panicles that are commonly self-pollinating (cleistogamous), ensuring seed set even under poor pollination conditions. Spikelets are small (1–5 mm) and lack awns.
The roughly 74 accepted species are concentrated in the Americas, with highest diversity in eastern North America. The genus is particularly characteristic of the Gulf and Atlantic coastal plain flora.
Etymology
The name Dichanthelium derives from the Greek for "twice-flowering," an allusion to the genus's characteristic biphasic growth cycle in which plants produce a vernal flush of stem growth and an autumnal rosette phase, each potentially bearing inflorescences.
Distribution
The genus is centred in the Americas, with greatest species richness in eastern North America along the Gulf and Atlantic coastal plains. Disjunct inland populations, notably in the Chicago region, are regarded as relictual coastal-plain elements. A smaller number of species extend into Central and South America and the Caribbean.
Ecology
Many species occupy open, sandy, or seasonally dry habitats characteristic of coastal plain communities, including pine savannas, oak barrens, and bogs. The production of cleistogamous secondary panicles is an ecological adaptation that guarantees seed set in low-pollinator or disturbed environments. In the Chicago region, Dichanthelium species are indicators of rare disjunct coastal-plain habitats.
Taxonomy Notes
Dichanthelium was separated from Panicum in 1974 after morphological and later molecular studies indicated the two groups are not closely related despite their similar spikelet form. Some regional flora treatments still list species under Panicum. GBIF currently recognises the genus as accepted with approximately 74 descendants.
