Calycoseris is a small genus of two species of annual desert wildflowers belonging to the family Asteraceae (order Asterales). The genus was described by Asa Gray in 1853 and contains only two accepted species: the yellow tackstem (Calycoseris parryi) and the white tackstem (Calycoseris wrightii). Both are native to the warm deserts and arid shrublands of the southwestern United States and northwestern Mexico.
The plants are low-growing annuals, typically 5–30 cm tall, with a taproot and one to three erect or ascending stems branching from the base. The most distinctive feature of the genus — and the source of the common name "tackstem" — is a covering of short, stipitate, flat-topped glands on the upper stems, branches, and involucral bracts that closely resemble thumbtacks. Leaves are alternate and sessile; basal leaves are pinnately lobed with narrow, linear, spreading lobes, while upper stem leaves are reduced to simple linear bracts.
Flower heads are borne singly or in open, cymiform arrays. Each head carries approximately 25 florets with showy ligulate corollas that are either white (C. wrightii) or yellow (C. parryi). The fruit is a tan-to-brown fusiform cypsela with five ribs and a slender beak tipped by a pappus of 50–60 or more white, basally connate, smooth bristles. The base chromosome number is x = 7.
Etymology
The genus name Calycoseris derives from the Greek kalyx (calyx, cup) and seris (a type of chicory or lettuce), referencing the cup-shaped involucre and the genus's placement in the chicory tribe (Cichorieae) of the daisy family. The common name "tackstem" refers to the distinctive tack-shaped glandular hairs that cover the upper stems and bracts of both species.
Distribution
Calycoseris is native to the warm deserts and arid regions of the southwestern United States — including California, Arizona, Nevada, Utah, New Mexico, and Texas — and extends into northwestern Mexico (Sonora and Baja California). Both species are plants of desert washes, sandy flats, and rocky slopes typical of the Mojave, Sonoran, and Chihuahuan desert systems.
Ecology
Both species of Calycoseris are winter annuals that germinate after autumn and winter rains and complete their life cycle in spring. They are typical components of low-elevation desert communities dominated by creosote bush and other desert shrubs, growing in sandy or gravelly soils of desert washes, bajadas, and disturbed open flats. The showy ligulate flowers are adapted for pollination by bees and other insects active in early spring.
