Perennials, 5-250 cm; taprooted, often producing offshoots connected by slender rhizomes. Stems 1-5, usually erect, sometimes decumbent (P. bootii), usually simple (leafy), usually glabrous proximally, tomentulose distally. Leaves basal and cauline; petiolate or sessile; blades deltate to triangular, or ovate to oblanceolate, or oblong to linear, or spatulate, margins often pinnately or palmately lobed (sometimes deeply cleft and appearing compound), ultimate margins entire or coarsely serrate or dentate (apices acute, obtuse, or rounded; distal leaves reduced in size and lobing. Heads (usually nodding at flowering) in racemiform, paniculiform, thyrsiform, or corymbiform arrays. Peduncles not inflated distally, bracteate. Calyculi of 2-12, triangular to linear-lanceolate or subulate, unequal bractlets. Involucres narrowly cylindric to campanulate (bases often attenuate), 2-14 mm diam. Phyllaries 3-15 in 1 series, (yellow green or green to purple or blackish) subulate or linear to lanceolate or elliptic, equal, margins scarious, apices acute, faces glabrous, tomentulose, hispid, or coarsely setose. Receptacles slightly convex, smooth, glabrous, epaleate. Florets 4-38; corollas usually creamy white, pink, or lavender, rarely yellow or red (glabrous). Cypselae golden brown to light tan, narrowly subcylindric, or fusiform to oblanceoloid, or oblong to linear, subterete or angled, apices truncate, not beaked, faces finely 5-12-ribbed, usually glabrous; pappi persistent, of 30-50, dull white to yellow or tan, rarely reddish brown, ± equal, barbellulate bristles in 1 series. x = 8.
Prenanthes is recognized by the erect and simple habit, deeply divided proximal leaves, whitish, yellow, or pinkish corollas in nodding heads, calyculate involucres, and pappi of barbellulate bristles. Leaf shape, size, and degree of lobing are often used for distinguishing species but are sometimes exceptionally variable. The proximal leaves are usually different in size, shape, and lobing from the distal leaves. Other taxonomic characters include size and habit, corolla color, number of florets per head, and phyllary number, color, and indument. The cypselae and pappi tend to be uniform.
Molecular ITS studies by S. C. Kim et al. (1996) suggested that Prenanthes, as here circumscribed, may be polyphyletic; additional sampling including North American taxa is needed to confirm the relationships of Prenanthes and recognition of Nabalus Cassini at the genus level.
Fls all ligulate and perfect, 5-35, pink or purple to white or pale yellow, the cor-tube more than half as long as the ligule; invol cylindric or seldom campanulate, of 4-15 principal bracts and some ±reduced outer ones; receptacle small, naked; achenes elongate, ±cylindric, glabrous, mostly reddish-brown, in our spp. ±ribbed striate; pappus of numerous deciduous capillary bristles; perennial herbs with milky juice, slightly to strongly tuberous- thickened roots, well developed alternate lvs (the larger ones at least 1 cm wide) and corymbiform or paniculiform to thyrsoid or subracemiform infl, the heads nodding or less often ±erect. 27, mainly N. Amer. and Eurasia. (Nabalus)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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