Columbian white-topped aster

Aster curtus Cronquist

Plants 19–37 cm. Stems erect, puberulent. Leaves basal and proxi-malmost cauline withering by flowering; cauline sessile; blades obovate, 10–60 × 3–9 mm, margins entire, apices acute, distal acuminate, faces puberulent. Heads 2–3 per branch, in compact corymbi-form arrays. Peduncle bracts ovate, puberulent. Involucres 6–9 mm. Phyllaries in 3–4 series, outer 3–5 mm, mid 5–7 mm, puberulent. Ray florets 1–2; corolla tubes 2–4 mm, laminae 2–3 mm. Disc florets 9–17; corolla tubes 4–6 mm, lobes 0.6–1 mm. Ovaries fusiform-obconic, 1–2 mm, strigose; pappi: inner series 6–7 mm.

Flowering mid summer–early fall. Prairie habitats, dry pastures, dry grassy Garry oak forests with rocky outcrops; of conservation concern; 10–200 m; B.C.; Oreg., Wash.

Sericocarpus rigidus grows on the southern part of Vancouver Island, British Columbia, and in scattered locations to the south end of the Puget Sound area in Washington. It is rare throughout its range and is listed as threatened in Canada, as Species of Concern by the U. S. Fish and Wildlife Service, as Sensitive in Washington, and as Threatened in Oregon. It is in the Center for Plant Conservation’s National Collection of Endangered Plants.