Braya humilis subsp. maccallae

Stems ascending to erect, often unbranched, 0.4-2.3 dm, moder-ately pubescent. Leaves: blade margins entire or, sometimes, sinuate-dentate, surfaces glabres-cent to moderately pubescent. Flowers: petals white, (4.4-)4.9-6.7(-7.2) × (2.1-)2.3-4(-4.2) mm. Fruits often abortive, somewhat torulose, 0.7-1.2 mm wide when fully developed; septum not fenestrate or split longitudinally. 2n = 28.

Flowering May-Jul. Sandy gravelly riverbanks and floodplains, sometimes on slopes and glacial moraines; 1500-3000 m; Alta., B.C.

Subspecies maccallae differs from subspp. elesmerensis and humilis in having leaf margins mostly entire, flowers exceptionally large, and a high percentage of abortive fruit. Cauline leaves are much reduced and arise from the base of the stem, giving an almost acaulescent appearance to the plant. Breeding studies (J. G. Harris 1985) indicate that subspp. maccallae and porsildii are self-incompatible, while most subspecies of Braya humilis are strongly autogamous.