Herbs, perennial, cespitose, pale to olive green or dark brown to bronze when dry, to 5 dm, not glaucous; rhizomes scarcely discernable. Stems simple, obviously winged, (1.5-)2-3.7 mm wide, glabrous, margins entire (in eastern populations) to denticulate (in western populations) apically, similar in color and texture to stem body. Leaf blades glabrous, bases not persistent in fibrous tufts. Inflorescences borne singly; spathes usually green or bronze, rarely with purplish margins, glabrous, keels usually denticulate; outer 36-76 mm, 12-46 mm longer than inner, slightly constricted proximal to apex, margins basally connate 2-5.7 mm; inner with keel ± gibbous basally, sinuous proximally, hyaline margins 0.1-0.3 mm wide, apex acuminate to acute, ending 0.9-4.3 mm proximal to recurved green apex. Flowers: tepals dark bluish violet, bases yellow; outer tepals 9-14.5 mm, apex emarginate to retuse, aristate; filaments connate ± entirely, stipitate-glandular basally; ovary similar in color to foliage. Capsules tan to dark brown, sometimes with purplish tinge apically, ± globose to obovoid, 4-6.8 mm; pedicel erect to spreading. Seeds globose to obconic, lacking obvious depression, 0.9-1.5 mm, rugulose.
Eastern coastal populations of Sisyrinchium montanum appear to have some slight affinity to S. angustifolium (e.g., long connation of outer spathe) and some previous floras have combined the two taxa. Some taxonomists have questioned the recognition of varieties within S. montanum, but we feel that the differences between them are no more subtle than those between varieties generally recognized elsewhere in the genus. Living material was not available to us to investigate breeding barriers. Although Sisyrinchium montanum is considered weedy by D. T. Patterson et al. (1989), I have seen many populations all through the western states and Great Lakes areas and would not consider it weedy in any of these portions of the range.
Erect, 1-5 dm, light green and glaucescent, drying pale, or deep green and drying dark; stems usually stout, flattened and winged; 1.5-3+ mm wide, the margins minutely denticulate, as also the lvs; largest lvs 2-3 mm wide; spathes mostly solitary at the summit of the simple stem, mostly not geniculate, usually green, the outer bract 3-7 cm, it s margins connate for 2-5 mm near the base, the inner bract much shorter, 1.5-3 cm; tep 8-12 mm, bright violet; fr 4-6 mm; 2n=32, 96. Sandy open ground and meadows; Que. to Alta., s. to N.Y., N.J., Pa., and Nebr., and along the mts. to Va. and N.C. (S. angustifolium, misapplied) The phase with the herbage blackening in drying has been called var. crebrum Fernald.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.