Thalictrum

1. Flowers few in an umbellate inflorescence (occasionally solitary); the perianth white to pink and much more conspicuous than the stamens.

T. thalictroides

1. Flowers numerous per inflorescence (6 to many in a panicle); stamens or carpels the most conspicuous part of the flower.

2. Upper cauline leaves long-petioled; leaflets glabrous and eglandular; blooming in April or May, before the leaves are fully expanded.

T. dioicum

2. Upper cauline leaves sessile or nearly so (the three main divisions on stalks appearing to be 3 petioles at a node); leaflets glabrous, pubescent, or with short-stalked glands; blooming June–July (–September), after the leaves are fully expanded.

3. Leaflets (especially on middle and lower leaves) with 2 or all 3 of the lobes again toothed or lobed, glabrous to sparsely glandular beneath.

T. venulosum

3. Leaflets mostly 3-lobed without additional teeth, usually pubescent or glandular beneath.

4. Fruit and undersides of leaflets with sessile or short-stalked glands.

T. revolutum

4. Fruit and leaflets not glandular, the leaflets usually ± pubescent beneath with multicellular hairs.

5. Longest mature anthers (1.5–) 1.6–2.5 (–3.4) mm long; longer stigmas mostly 2.2–3.6 mm long.

T. dasycarpum

5. Longest mature anthers 0.9–1.4 (–1.5) mm long; longer stigmas mostly 1–2.1 mm long.

T. pubescens