45. Prenanthes L. (rattlesnake root, white lettuce)

(Milstead, 1964)

Contributed by David J. Bogler and George Yatskievych

Plants perennial herbs, usually with somewhat tuberous-thickened rootstocks, often producing offsets and then colonial. Latex white. Stems usually solitary, erect or ascending, finely to less commonly coarsely ridged, glabrous or variously hairy. Leaves alternate and basal, mostly 1–3 times as long as wide, or, if 3–5 times as long as wide, then the blade tapered abruptly to a winged petiole, glabrous or hairy, sessile to long-petiolate, the basal leaves mostly withered before flowering (except in P. racemosa), the stem leaves not clasping the stem or the rounded bases somewhat clasping. Leaf blades often quite variable on the plant, unlobed to 3-lobed or shallowly pinnately lobed, variously shaped, the margins entire or finely to coarsely toothed, sometimes irregularly so. Inflorescences consisting of small clusters, these appearing axillary and/or terminal, the terminal ones often arranged into narrow, spicate or broad, open panicles. Involucre not or only slightly elongated at fruiting, narrowly cylindrical to narrowly bell-shaped or urn-shaped, the bracts in 1 long inner and 2 or 3 shorter outer series, those of the inner series all similar, narrowly oblong-elliptic to narrowly oblong-lanceolate, those of the outer series ovate to narrowly lanceolate, sometimes purplish- or reddish-tinged, glabrous or hairy, the margins sometimes thin and pale, the tip appressed-ascending at flowering. Receptacle naked. Ligulate florets 4–35 per head. Corollas white, yellow, pink, or purple. Pappus of numerous bristles, these straw-colored to tan, orangish brown, or reddish brown, often shed irregularly at fruiting. Fruits with the body nearly cylindrical to narrowly oblong-elliptic in outline, more or less circular in cross-section or sometimes 4- or 5-angled, not flattened, not beaked, the pappus attached to an unmodified or only slightly expanded tip, often (8–)10–12-ribbed, the surface otherwise relatively smooth, yellowish brown to reddish brown. Twenty-six to 30 species, North America, Europe, Asia, Africa.

The present treatment uses the traditional broad circumscription of the genus. However, in a preliminary phylogenetic study of molecular data, Kim et al. (1996) found that Prenanthes may actually consist of three species groups that are only distantly related within the subtribe Sonchinae K. Bremer. If future research yields similar results, then the name Prenanthes must remain with a group of about nine Old World species related to the type species, P. purpurea L. The Macaronesian P. pendula Sch. Bip. is isolated in the second group. The approximately 14 species in North America form the third group and would have to be restored to a separate genus under the name Nabalus Cass.