Thalictrum L. (Ranunculaceae)

Thalictrum is represented by eight species in North Carolina. Two species species are currently listed: Thalictrum cooleyi (Fed E, S1 G1) and T. macrostylum (State SC-V, S2 G3G4).

Thalictrum is a difficult genus, requiring additional taxonomic study. Workers have held rather different taxonomic concepts (see Keener 1976 vs. Park & Festerling 1997). Several taxa—particularly T. pubescens and T. coriaceum—remain problematic (see Park 1992).

Note that Thalictrum species in general tend to be much more common in the mountains and Piedmont, than in the Coastal Plain.  

Federally listed taxon—
Thalictrum cooleyi(Fed E, State E | S1 G1)

Habitat. Grass-sedge bogs, wet pine savannas.

Range. Endemic to SE Coastal Plain (FL, GA, NC).

Notes. Thalictrum represents a difficult genus in need of much additional population level research. A problem of particular interest to North Carolina workers, is the resolution of taxonomic issues in the T. revolutum-T. pubescens complex. Some authors have recognized multiple taxa in this complex, whereas others only few (see Weakley 2010 for more detailed discussion). Weakley (2010) decided to provisionally recognize T. pubescens var. hepaticum at the varietal level to draw attention to the problem--a decision followed here as well.

Additional resources. NHP | Recovery plan

Key to Thalictrum in North Carolina

Key adapted from Radford et al. (1968) and Weakley (2008, 2010). Photos by Krings, unless otherwise indicated. Line drawings from Britton & Brown (1913). Maps courtesy of USDA PLANTS and the North Carolina Natural Heritage Program.

1. Leaflets of the stem leaves linear to narrowly lanceolate, oblanceolate, or elliptic, (3–) 5–10 (–25) x as long as wide...T. cooleyi*

1’. Leaflets of the stem leaves ovate, obovate, or suborbicular, 0.7–3 (–5) x as long as wide...2.

2. Inflorescence umbellate... T. thalictroides

2’. Inflorescence paniculate...3.

3. Achene scimitar-shaped; flowers perfect...T. clavatum

3’. Achene not scimitar-shaped; flowers unisexual or sometimes a few bisexual...3.

4. Most leaflets with (3–) 4–6 (–9) lobes or teeth...5.

5. Cauline leaf subtending the lowest flowering branch sessile; plant flowering May–Jul...T. coriaceum

5’. Cauline leaf subtending the lowest flowering branch with a petiole 3–7 cm long; plant flowering Mar-Apr
...T. dioicum

4’. Most leaflets with 1–3 (–5) lobes or teeth...6.

6. Abaxial leaflet surface, peduncles, and achenes with stipitate glands or papillae...7.

7. Anthers 0.5–1.2 mm long; stigmas 0.6–2.2 mm long...T. pubescens var. hepaticum

7’. Anthers 1.5–2.8 mm long; stigmas (1.5–) 2.0–3.5 mm long...T. revolutum

6’. Abaxial leaflet undersurfaces, peduncles, and achenes glabrous or pubescent, but lacking both stipitate glands and papillae...8.

8. Abaxial leaflet surfaces, peduncles, and achenes finely pubescent...T. pubescens var. pubescens

8’. Abaxial leaflet surfaces, peduncles, and achenes glabrous...9.

9. Leaflets entire to 3-lobed, largest usually < 22 mm wide; filaments (2–) 3–4.5 (–6.5) mm long...T. macrostylum

9’. Leaflets 3-lobed (rarely entire), largest usually 15–60 mm wide; filaments (2–) 4–5 (–8) mm long...10.

10. Anthers 0.5–1.2 mm long; stigmas 0.6–2.2 mm long...T. pubescens var. hepaticum

10’. Anthers 1.5–2.8 mm long; stigmas (1.5–) 2.0–3.3 mm long...T. revolutum