Froelichia, commonly known as snakecotton, is a genus of herbs and occasionally shrubs in the family Amaranthaceae, order Caryophyllales. The genus comprises roughly 13–15 species native to the Americas, with two species endemic to the Galápagos Islands.
Plants are annual or perennial, with erect or procumbent stems that are simple to much-branched, sometimes broomlike in habit, and usually richly pubescent. Leaves are opposite, mostly sessile or short-petiolate, and are most abundant on the lower half of the plant; the blades are linear to orbiculate, often fulvous (tawny) on the lower surface, with entire pubescent margins. The inflorescences are terminal, pedunculate spikes, either elongated and interrupted or rounded and head-like, with a woolly or silky rachis of spirally arranged bracts each subtending two concave bracteoles that enclose and fall with the flowers.
The flowers are bisexual, with five tepals fused at least halfway into a tube that is two-lipped and five-lobed. In fruit the tube becomes indurate (hardened) and develops lateral wings or crests — a distinctive feature of the genus — and in some species bears facial tubercles or spines. The five stamens have filaments fused into a cylindric tube with alternating pseudostaminodes; anthers are two-locular. Each flower produces a single-seeded, indehiscent utricle enclosed within the hardened perianth tube. The base chromosome number is x = 8.
Froelichia is most abundant in the Sonoran and Chihuahuan deserts, the plains of southern Texas and Florida, and the grasslands of eastern Paraguay and southern Brazil. Species are pioneers of disturbed sandy soils and are characteristic of coastal pine habitats along the Gulf Coast. The genus is perhaps best known as a roadside weed; F. gracilis has spread widely across the United States, and F. floridana became naturalized in Queensland, Australia, most likely via contaminated seed in the mid-1950s.
Etymology
The genus name Froelichia honors Joseph Aloys von Froelich (1766–1841), a German physician and botanist. The common name "snakecotton" refers to the woolly, cotton-like texture of the flower spikes.
Distribution
Froelichia is centered in the Americas, with greatest diversity in the Sonoran and Chihuahuan deserts, the coastal plains of southern Texas and Florida, and the grasslands of eastern Paraguay and southern Brazil. Two species, F. lanigera and F. nudicaulis, are endemic to the Galápagos Islands. Several species have spread beyond their native ranges: F. gracilis has been introduced throughout much of the United States, and F. floridana is naturalized in Queensland, Australia.
Ecology
Froelichia species are pioneers of disturbed, sandy soils and thrive in environments with low competition. They are common constituents of coastal pine woodlands along the Gulf Coast, and frequently colonize roadsides, fallow fields, and pastures, occasionally becoming minor agricultural weeds in row crops.
Taxonomy Notes
The genus is divided into two sections: sect. Hoplotheca (Nuttall) Moquin-Tandon, with capitate stigmas, occurring in both North and South America; and sect. Dilopha Moquin-Tandon, with penicillate stigmas, restricted to South America. Phylogenetically, two principal clades occur across North America: a perennial clade centered on F. interrupta ranging from the southern US through Mexico to Nicaragua, and a northern clade of mixed annual and perennial species. Revisionary work by R. A. McCauley (2002) recircumscribed species limits and geographic ranges, identifying more stable diagnostic characters in place of the previously over-used, highly variable lateral wing morphology of the mature perianth.
