Boott’s rattlesnakeroot

Nabalus boottii de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 7: 241. 1838 (‘bootii’)

Plants 5–25 cm; taproots short, thick, tuberous. Stems decumbent to erect, mottled purple, simple, glabrous proximally, tomentulose distally. Leaves: proximal present at flowering; petiolate (petioles 2–8 cm, not winged); blades ovate to deltate, 2–8 × 0.5–3 cm, bases hastate or sagittate, margins entire or weakly dentate, faces glabrous; distal reduced, elliptic to lanceolate. Heads (10–20) in narrow, racemiform to thyrsiform arrays (nodding). Calyculi of 4–5, dark green to blackish, subulate bractlets 2–5 mm, glabrous. Involucres cylindro-campanulate, 10–11 × 5–6 mm. Phyllaries 8–11, dark green to almost black, lanceolate to subulate, 8–12 mm, faces glabrous. Florets 9–20; corollas white, 7–13 mm. Cypselae light tan to yellow, subcylindric, subterete to angled, 5–6 mm, indistinctly 7–10-ribbed; pappi pale yellow, 6–8 mm. 2n = 32.

Flowering Jul–Aug. Alpine areas above treeline, mountains; of conservation concern; 1500–2000 m; Maine, N.H., N.Y., Vt.

Prenanthes boottii is recognized by its relatively short, decumbent habit, deltate to hastate proximal leaves, entire or weakly dentate margins, glabrous and blackish green phyllaries, white corollas, and alpine habitat.