Herbs, perennial, slightly cespitose, dark olive when dry, to 4.2 dm, not glaucous; rhizomes scarcely discernable. Stems simple, obviously winged, 2.2-3.5 mm wide, glabrous, margins denticulate, similar in color and texture to stem body. Leaf blades glabrous, bases not persistent in fibrous tufts. Inflorescences borne singly; spathes green, glabrous, keels entire or denticulate; outer 36-58 mm, 6-39 mm longer than inner, tapering evenly towards apex, margins basally connate 4.5-7 mm; inner with keel evenly curved, hyaline margins 0.2-0.5 mm wide, apex acute, ending 0.2-2 mm proximal to green apex. Flowers: tepals light blue to usually deep bluish violet, bases yellow; outer tepals 11-16 mm, apex rounded to slightly truncate, aristate; filaments connate ± entirely, stipitate-glandular basally; ovary similar in color to foliage. Capsules beige to dark brown, ± globose, 6.2-8.1 mm; pedicel erect to ascending. Seeds globose to obconic, lacking obvious depression, 1.2-1.7 mm, rugulose. 2n = 96.

Flowering spring--mid summer. Moist, sandy or grassy areas near coast, interdunal depressions, edges of streams and lakes; 0--300 m; B.C.; Alaska, Wash.

Populations of Sisyrinchium littorale in coastal Washington and on Vancouver Island, British Columbia, intergrade with S. idahoense var. segetum. Sisyrinchium littorale, however, has larger capsules and wider stems and leaves.