Humboldt Mountains or pallid or Davis’s or jewel milkweed

Asclepias davisii Woodson, Ann. Missouri Bot. Gard. 26: 261, fig. 1. 1939; A. cryptoceras var. davisii (Woodson) W. H. Baker

Leaves: petiole 2–8 mm; blade oval to ovate or obovate or orbiculate, 3–7 × 1.8–4.8 cm, apex rounded to acute, venation eucamptodromous, surfaces gla­brous. Inflorescences 3–8-flowered. Pedicels 16–25 mm. Flowers: calyx lobes 5–6 mm; corolla lobes 8–11 mm; fused anthers dark brown, green at apex, 1.8–2.5 mm; corona segments pinkish purple, 5–6(–7) mm, apices (including recurved tooth) exceeded by or equaling style apices.

Flowering Apr–Jul; fruiting May–Jul. Slopes, hills, arroyos, basalt, silicic tuff, limestone, chert, serpentine, gravel, sand and clay soils, juniper woodlands, shrubby grasslands, steppe; 300–1500(–2100) m; Calif., Idaho, Nev., Oreg., Wash.

Subspecies davisii just enters Washington in Asotin County and is exceedingly rare in the state, where it is considered to be of conservation concern.