Stephanomeria malheurensis L. D. Gottlieb

Stephanomeria malheurensis has been examined in a series of studies (L. D. Gottlieb 1973b, 1977, 1978b, 1979, 1991; Gottlieb and J. P. Bennett 1983; S. Brauner and Gottlieb 1987, 1989; B. A. Bohm and Gottlieb 1989) because it is one of the very few examples of the recent, natural origin of a diploid, annual plant species. At the type locality, it grows with a population of S. exigua subsp. coronaria that is thought to be its progenitor.

Stephanomeria malheurensis is known from a single locality in Harney County, Oregon, growing in soil derived from volcanic tuff in the high desert of eastern Oregon. It is a federally listed rare and endangered species, and is in the Center for Plant Conservation’s National Collection of Endangered Plants.

Annuals, 10–60 cm. Stems single, branches ascending, glabrous. Leaves withered at flowering; basal blades oblanceolate to spatulate, 5–7 cm, margins entire to pinnately lobed (faces glabrous); cauline much reduced, bractlike. Heads borne singly along branches. Peduncles 5–10 mm (glabrous). Calyculi of appressed bractlets. Involucres 8–9.5 mm. Florets 5–6 (ligules usually pink, rarely white or orange-yellow). Cypselae tan to light brown, 3.3–3.8 mm, faces moderately tuberculate, grooved; pappi of 9–12(–15), light tan bristles (connate in groups of 2–4, bristles and/or bases persistent), plumose on distal 50–60%. 2n = 16.