Abstract
Gamochaeta Wedd. (Asteraceae, Gnaphalieae) is a New World genus with a center of diversity in South America. The genus is characterized by capitula usually arranged in spikes or headlike clusters; pistillate florets outnumbering the bisexual florets; truncate style branches with apical sweeping trichomes; pappus bristles connate at the base into a ring that falls as a unit; and achenes with usually globose twin trichomes. We present here the first morphometric analysis of this genus. Based upon these results, 53 species are recognized, and two are newly synonymized: G. neuquensis Cabrera under the name G. chamissonis (DC.) Cabrera, and G. impatiens G. L. Nesom under the name G. americana (Mill.) Wedd. A lectotype is newly designated for Gnaphalium spiciforme Sch. Bip. The occurrence in southern Argentina of Gamochaeta procumbens (Phil.) Cabrera is reported for the first time, and G. standleyi (Steyerm.) G. L. Nesom is new for Colombia. One species, Gamochaeta thouarsii (Spreng.) Anderb., is treated as dubious. A key to the species is provided, as well as morphological descriptions, synonymy, distribution and habitat information, distinguishing characters, taxonomic affinities, distribution maps, illustrations of the species, and additional material examined.
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