White pincushion

Acarphaea artemisiifolia Harvey & A. Gray, Mem. Amer. Acad. Arts, n. s. 4: 98. 1849 (as artemisiaefolia)

Plants (15–)25–90(–200) cm. Leaves basal (withering) and cauline, 3–15(–20) cm; largest blades ± plane, not succulent; primary lobes mostly 5–10 pairs, ultimate lobes ± crowded, antrorse, lanceolate to elliptic, plane. Peduncles 1.5–6 cm. Involucres ± hemispheric, mostly 10–15 mm diam. Phyllaries: longest 7–10(–12) mm, ± densely villous, not or sparsely glandular; apices (all) erect, ± green, acute or scarcely acuminate, not aristate, ± plane. Receptacles: paleae 0. Corollas 5–7 mm. Cypselae compressed, 4–7 mm; pappi 0 or coroniform (of ± 10 scales, longest 0.1–0.5 mm). 2n = 16.

Flowering Apr–early Jul. Dry canyons, open slopes, often over granitoid rocks, locally abundant in chaparral burns or other recovering disturbances; 80–1600 m; Calif.; Mexico (Baja California).

In the flora area, Chaenactis artemisiifolia is known from the Transverse and Peninsular ranges and seaward valleys of southwestern California. It is fire-adapted; its germination is significantly enhanced by exposure to biomass smoke (J. E. Keeley and C. J. Fotheringham 1998).

Chaenactis lacera Greene, the eighteenth species of the genus, is known from coastal portions (including islands) of the western Vizcaíno Desert in Baja California and Baja California Sur, Mexico. Forms of C. artemisiifolia sometimes resemble C. lacera in coastal southern California (P. Stockwell 1940), where C. lacera could eventually be introduced. Besides the key characteristics above, C. lacera differs from C. artemisiifolia by its largest leaf blades broadly ± elliptic, 2–3-pinnately lobed, ultimate lobes remote, recurved to retrorse, ± linear, involute (leaf blades appearing ± skeletal).