Gamochaeta is a genus of flowering plants in the family Asteraceae (order Asterales), commonly known as cudweeds or everlastings. The genus is native to North and South America, with one species endemic to the remote island of Tristan da Cunha in the South Atlantic. A number of species have become established outside their native ranges as introduced or invasive weeds in other parts of the world.
The genus was long contentious: many of its species were formerly included in the closely related genus Gnaphalium, and botanists did not always agree on whether Gamochaeta merited separate recognition. In recent decades, however, it has gained wider acceptance as a distinct genus based on a suite of consistent morphological characters.
Plants of Gamochaeta are herbaceous annuals or perennials, typically woolly or cottony in texture. They are distinguished by their relatively small flower heads arranged in spiciform (spike-like) arrays, concave receptacles after the fruits have dispersed, and bisexual florets with truncate collecting appendages on the style branches. The small dry fruits (cypselae) bear minute papilliform hairs on their faces that produce mucilage, and the pappus bristles are fused at their bases into smooth rings and shed as a single unit rather than individually — a character that helps separate Gamochaeta from Gnaphalium.
Distribution
Gamochaeta is native to North and South America. One species is endemic to Tristan da Cunha, a remote island in the South Atlantic Ocean. Several species have been introduced beyond their native ranges and can occur as invasive weeds in agricultural and disturbed habitats worldwide.
Taxonomy Notes
Gamochaeta has had an uncertain taxonomic history. Many of its species were formerly placed in Gnaphalium, and recognition of the genus was long debated among botanists. It has become more broadly accepted as a distinct genus in recent years, separated from Gnaphalium by consistent morphological characters including the structure of the pappus bristles and the form of the cypselae.
