Thysanocarpus laciniatus is very similar to
thysanocarpus curvipes, differing in the cauline leaves, which are narrowly elliptic, widest around the middle, and are not clasping at the base; the other species has leaves widest at the base, and clasping. Mountain fringepod leaves are glabrous or sparsely hairy (hairs are short and white), and they have a few small, well-separated pinnate lobes along the margin, unlike thysanocarpus curvipes for which the margins are unlobed. Stems are somewhat glaucous, and usually hairless.
The inflorescence is an elongated, unbranched cluster, with alternately-arranged flowers. Sepals are greenish-white, the petals pure white, and the anthers purple. Fruits are ovate to round, pale green, sparsely hairy to glabrous, on smoothly curved pedicels, angled downwards. Fruit margins may be entire, or shallowy to deeply toothed, or perforated.