91. PRENÁNTHES, Vaill. Rattlesnake-root.
Heads 5–30-flowered. Involucre cylindrical, of 5 to 14 linear scales in a single row, and a few small bractlets at base. Achenes short, linear-oblong, striate or grooved, not contracted at the apex. Pappus of copious straw-color or brownish and rough capillary bristles.—Perennial herbs, with upright leafy stems arising from spindle-shaped (extremely bitter) tubers, very variable leaves, and racemose-panicled mostly nodding heads. Flowers greenish-white or yellowish, often tinged with purple; late summer and autumn. Our species belong to the subgenus Nábalus. The original European species has soft white pappus. (Name from πρηνής, drooping, and ἄνθη, blossom.)
[*] Heads rather broad, 25–35-flowered, in a corymbose panicle.
1. P. crepidínea, Michx. Somewhat smooth; stem stout (5–9° high), bearing numerous nodding heads in loose clusters; leaves large (6–12´ long), broadly triangular-ovate or halberd-form, strongly-toothed, contracted into winged petioles; pappus brown. (Nabalus, DC.)—Rich soil, Penn. and western N. Y. to Minn., and southward.—Flowers cream-color.
[*][*] Heads narrow, 8–15-flowered, in a long raceme-like or thyrsoid inflorescence; stems simple; cauline leaves sessile; pappus straw-color.
[+] Inflorescence pubescent, strict; heads nearly erect, 12–15-flowered.
2. P. racemòsa, Michx. Stem 2–5° high, smooth and glaucous, as well as the oval or oblong-lanceolate denticulate leaves; the lower tapering into winged petioles (rarely cut-pinnatifid), the upper partly clasping; heads in crowded clusters; flowers purplish. (Nabalus, DC.)—Plains, N. Maine to N. J., Mo., and northward.—Var. pinnatífida, Gray, the leaves all lyrately pinnatifid. Hackensack marshes, N. J.
3. P. áspera, Michx. Stem 2–4° high, rough-pubescent, as well as the oval-oblong or broadly lanceolate toothed leaves; upper leaves not clasping; heads in small clusters; flowers larger, cream-color. (Nabalus asper, Torr. & Gray.)—Dry prairies and barrens, Ohio to Iowa, and southward.
[+][+] Whole plant glabrous; heads nodding, 8–12-flowered; thyrse looser.
4. P. virgàta, Michx. (Slender Rattlesnake-root.) Slightly glaucous; stem 2–4° high, prolonged into a naked and slender spiked raceme (1{½}–2° long); heads clustered and mostly unilateral; leaves lanceolate, acute, closely sessile, the upper reduced to bracts, the lower toothed or pinnatifid; involucre (purplish) of about 8 scales. (Nabalus, DC.)—Sandy pine barrens, N. J. to Va., and southward.