Thelesperma, commonly called greenthreads, is a genus of annual or perennial herbs and subshrubs in the daisy family Asteraceae. It was first described by the German botanist Christian Friedrich Lessing in 1831 in the journal Linnaea and currently comprises around 12 accepted species, distributed across the Americas from Alberta, Canada, through the United States and Mexico, and extending south to Argentina and Uruguay.
Plants typically grow between 10 and 70 cm tall and bear opposite leaves with pinnately lobed, usually hairless blades that may be largely basal or largely stem-borne depending on the species. Flower heads are radiate or discoid, borne singly or in loose, flat-topped (corymbiform) arrays. Each head may carry up to eight ray florets in yellow, reddish-brown, or yellow-and-brown bicolored tones, surrounding 20 to more than 100 yellow or brown disc florets; a few species lack ray florets entirely.
The genus is closely related to Coreopsis and to certain North American Bidens species, including Bidens coronata and Bidens comosa. Several species have long been used by southwestern Native American peoples as an herbal tea, and Thelesperma megapotamicum is known to contain the flavonoid luteolin; the broader genus appears to share a similar flavonoid profile across species.
Etymology
The genus name Thelesperma derives from the ancient Greek words θηλή (thele, "nipple") and σπέρμα (sperma, "seed"), a reference to the nipple-like papillate surface of the cypselae (seed-like fruits) found in some species. In English the genus is commonly known as greenthreads.
Distribution
Thelesperma ranges from Alberta, Canada, south through the United States and into northern and western Mexico, and also occurs in South America from Argentina to Uruguay. The genus is therefore primarily concentrated in the grasslands, plains, and semi-arid scrublands of the Americas.
Taxonomy Notes
Thelesperma was established by Christian Friedrich Lessing in 1831 (published in Linnaea). It sits within the tribe Coreopsideae of the family Asteraceae and is considered most closely related to parts of Coreopsis and to certain North American Bidens species (including Bidens coronata and Bidens comosa). As of July 2023, Plants of the World Online accepts 12 species for the genus; GBIF lists 9 taxa.
Cultural Uses
Several Thelesperma species have been used by southwestern Native American peoples as an herbal tea, brewed from the stems. Thelesperma megapotamicum is the best-documented of these, and chemical studies confirm it contains the flavonoid luteolin. Broader analysis suggests many species in the genus share a similar chromatographic profile, indicating comparable flavonoid compositions across the group.
