Snake River or creeping twinpod

Physaria didymocarpa (Hooker) A. Gray var. integrifolia Rollins, Rhodora 41: 407. 1939; P. integrifolia var. monticola Lichvar

Perennials; caudex usually branched, (rhizomelike, ces-pitose); densely (silvery) pubescent, trichomes (often stalked, appressed), several-rayed, rays furcate or bifurcate, (umbonate, strongly tuberculate throughout). Stems several from base, ± erect, exceeding basal rosette by ± 0.5 dm. Basal leaves (forming a strong rosette; long-petiolate); blade oblanceolate to ovate or orbicular, (1.5-) 2-4(-8) cm, (base usually abruptly tapering to petiole), margins entire. Cauline leaves: blade oblanceolate, 1-2 cm, margin entire, (apex acute). Racemes congested, (greatly exceeding leaves). Fruiting pedicels (spreading, straight or slightly curved), 7-11 mm. Flowers: sepals often keeled, 6-8 mm; petals spatulate, 8-10 mm. Fruits didymous, highly inflated, 8-22 × 10-25 mm, (papery, basal and apical sinuses deep); valves (retaining seeds after dehiscence), densely pubescent, trichomes appressed; replum linear to oblong, as wide as or wider than fruit; ovules 8 per ovary; style 7-9 mm. Seeds flattened. 2n = 16.

Flowering (May-)Jun-Jul(-Aug). Calcareous hills and slopes, shale-limestone cliffs, bare steep slopes, red clay banks, shale; 1900-2700 m; Idaho, Mont., Wyo.

Physaria integrifolia has traditionally been recognized as a variety of P. didymocarpa, but it is morphologically and ecologically quite distinctive. Variety monticola (no combination has been made at subspecific rank) is not recognized here; it is considered another example, in the genus, of caudices elongating in response to shifting substrates.