Stems erect to reclining, slender, 60-200 cm. Leaves: proximal cauline petiolate, distal cauline sessile to nearly sessile; petioles and rachises glabrous, neither pubescent nor glandular. Leaf blade: proximal cauline mostly 2×-ternately compound, distal cauline usually ternately compound; leaflets linear to narrowly lanceolate or oblanceolate, apically occasionally 2-3-lobed, 12-68 × 1-12 mm, length (2.6-)4-26 times width, membranous to leathery, margins sometimes revolute, lobe margins entire; surfaces abaxially glabrous. Inflorescences racemes to panicles, elongate, few flowered; peduncles and pedicels neither pubescent nor glandular. Flowers usually unisexual, staminate and pistillate on different plants; sepals 4-5, white to yellowish in staminate flowers, greenish in pistillate flowers, obovate, 1.5 mm; filaments white to purple, 2.5-6 mm; anthers 0.9-2.5 mm. Achenes 5-6, sessile or nearly sessile; stipe 0-0.4 mm; body ellipsoid, 4.5-6 mm, prominently veined, glabrous; beak 1.3-2.4 mm. 2 n = 210.

Flowering summer (mid Jun-mid Jul). Boggy, savannahlike borders of low woodlands, and disturbed areas such as roadside ditches, clearings, and edges of frequently burned savannahs; of conservation concern

Thalictrum cooleyi occurs commonly on Grifton soil and is associated with some sort of disturbance, including clearings, edges of frequently burned savannahs, roadsides, and powerline rights-of-way that are maintained by fire or mowing. Silvicultural and agricultural practices and their associated suppression of fire have seriously affected populations of T . cooleyi . Furthermore, fruit production appears to be quite low in the species (S. W. Leonard 1987).

Leaves of Thalictrum cooleyi have fewer leaflets than other species of Thalictrum sect. Leucocoma .