The grass-like leaves of Sisyrinchium montanum
grow only at the base, and number two to six per stem. Leaves have faint lengthwise grooves. Stems are unbranched, hairless, flattened, and winged. The margins of the wings may be finely toothed. Leaf tips are pointed.
Flowers are produced singly or in a cluster of up to five. Flowers are formed of six tepals, yellow at the base, otherwise bluish purple, crossed by a few darker veins. Tepals are tipped by a narrow, inwards-curving projection. The styles and stamens are joined to form a tube at the center, purplish and glandular hairy towards the base. Beneath the flowers are a pair of unequal-length bracts.
Most specimens of sisyrinchium montanum are var montanum
; the less common var crebrum
is found only in the northeast of the US. The two varieties are distinguished via the relative lengths of the fused section of the margins of the longer of the two subtending bracts (the spathes).