16. Thalictrum heliophilum Wilken & DeMott, Brittonia. 35: 156. 1983.
Roots fibrous. Stems 14-50 cm, arising singly or in dense clusters of 2-3 from short, horizontal, fibrous-rooted rhizomes. Leaves basal and cauline, petiolate. Leaf blade ternately compound, cauline blades gradually reduced upward, distalmost 2-ternate; leaflets broadly obovate, apically 3-toothed, otherwise undivided, 5-8 × 4-5 mm, leathery, surfaces glabrous, glaucous. Inflorescences terminal, panicles, many flowered. Flowers: sepals 4, color unknown, lanceolate to ovate, 2-3 mm; filaments brownish, 2-3 mm; anthers 2-3 mm, apiculate; stigma color unknown. Achenes 4-5(-6), not reflexed, nearly sessile; stipe 0.1-0.2 mm; body oblique-obovate, strongly laterally compressed, 4-5 mm, glabrous, glaucous, prominently 3-veined on each side, veins converging near apex, rarely branched or sinuous, not anastomosing-reticulate; beak ca. 1.5 mm.
Flowering summer-summer (Jun-Aug). Decomposing shale of Green River Formation; of conservation concern; 2500 m; Colo.
In a genus of primarily mesophytic plants, Thalictrum heliophilum is notable for its relatively xeric habitat. Known only from Garfield and Rio Blanco counties, northwestern Colorado, it is similar to the widespread T . fendleri ; it may be distinguished by its smaller, leathery, glaucous leaflets and fewer achenes.