Description
Physaria scrotiformis is a long-lived perennial from a simple or sparsely branched underground caudex. While the fruit are rather distinctive (hence, the specific epithet), the flowers have not been seen. Plants are silvery-gray-green to silvery-purplish, the silver color due to a dense covering of trichomes. Stems are 0.8 to 3 cm long, unbranched, purplish, arising lateral (beneath) the erect or ascending tuft of basal leaves, prostrate to slightly decumbent, from stem tip to stem tip plants up to 10 cm, but typically less than 5.5 cm in diameter. Basal leaves are entire, oblanceolate, elliptic or rhombic, mostly flat, sometimes somewhat folded, attenuate at base and tapering to a slightly winged petiole. Apex rounded to rounded-acute, including the petiole, encrusted with trichomes. Cauline leaves are entire, elliptic to oblanceolate, short-petiolate to essentially entire, 3 to 7 per stem. Infructescence, not elongating appreciably, is a raceme with 3 to 7, more or less crowded fruits, these on straight, ascending pedicels 1.8 to 3.4 mm long. Silicles on stipes 0.2 to 0.5 mm long, ovoid to obpyriform, slightly but obviously didymous (especially in living material), apex rounded, flattened, or even slightly emarginate; base rounded-obtuse; wider than long; 3 to 4.5 mm long and 3.7 to 5 mm wide, the valves inflated and a little wider than the replum; valves glabrous within, the exterior with scattered tricomes; becoming purplish or greenish-purple at maturity; replum entire or medially small-perforate, obovate to rounded-obdeltoid, rounded to obtuse or truncate at the apex (O'Kane 2007).
Habitat
Grows on windswept, nearly barren exposures of Leadville limestone in a matrix of Picea engelmannii islands and tundra (O'Kane 2007). Associates on the nearly barren spots where the species occurs include Minuartia obtusiloba, Zigadenus elegans, Castilleja haydenii, Pseudocymopterus montana, Poa alpina, Hymenoxys grandiflora, Allium geyeri, Townsendia rothrockii and Trisetum spicatum. The plants grow in shallow soil between grey and tan-grey limestone cobbles (O'Kane 2007).