This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
S. tomentosus Michx. Fl. Bor. Am. 2: 119. 1803.
Perennial, more or less densely and persistently tomentose or woolly-canescent; stems rather stout, solitary, or sometimes tufted, 1°-2 1/2° high. Basal and lower leaves ovate-lanceolate, oblong or rarely spatulate, long-petioled, erect, very obtuse, 2'-6' long, ¥-2' wide, crenate-dentate, narrowed or truncate at the base; stem leaves few and distant, small, linear-lanceolate or spatulate, crenate or rarely laciniate; heads several or numerous, corymbose, mostly long-peduncled, 8"-10" broad; involucre cylindric, or narrowly campanulate, its bracts linear-lanceolate, acute or acuminate, at length glabrate, with or without a few small outer ones; rays 10-15; achenes hispidulous, at least on the angles; pappus white.
In moist soil, southern New Jersey to Florida, Louisiana, Texas and Arkansas. April-June.
Perennial, similar to the preceding species, usually smaller-leaved, lower and less tomentose, or becoming glabrate in age, seldom over 1 1/2° high. Basal leaves oval, ovate or oblong, some or all of them often more or less pinnatifid, with the terminal segment much larger than the lateral ones, crenulate or dentate, long-petioled; stem leaves mostly smaller than the basal ones, usually pinnatifid; heads several or numerous, compactly or loosely corymbose, conspicuously radiate.
Indiana and Illinois to Ontario, North Dakota, Colorado, Missouri and Texas. April-June.
Senecio pseudotomentosus Mackenzie & Bush, of Missouri, differs in having the basal leaves mostly merely dentate.
Perennial, glabrous or very nearly so throughout; stems slender, 1°-2 1/2° high. Basal leaves long-petioled, lanceolate, obtuse or acute at the apex, cordate, subcordate or truncate at the base, usually thin, 2-4' long, 1/2'-1 1/4' wide, sharply dentate; stem leaves mostly pinnatifid or lobed, at least below the middle; heads several or numerous, slender-peduncled in an open corymb. 8"-10" broad; rays 6-12; achenes glabrous or pubescent; pappus white.
In swamps and mountain meadows, Nova Scotia to New Hampshire, Vermont and New York. June-Sept.
Senecio aureus L. Sp. Pl. 870. 1753.
Senecio pauciflorus Pursh, Fl. Am. Sept. 529. 1814.
Senecio gracilis Pursh, Fl. Am. Sept. 529. 1814.
Perennial, glabrous or very nearly so throughout; stems rather slender, solitary or tufted, 6'-2 1/2° high. Basal leaves cordate-ovate or cordate-orbicular or reniform, crenate-dentate, very obtuse and rounded, often purplish, 1'-6' long, with long slender petioles; lower stem leaves lanceolate or oblong, usually laciniate, pinnatifid or lyrate, the uppermost small, sessile, somewhat auriculate and clasping; heads usually several, 8"-10" broad, 4"-5" high, slender-peduncled in an open corymb; rays 8-12, golden-yellow; achenes glabrous; pappus white.
In swamps and wet meadows, Newfoundland to Florida, Ontario, Michigan, Missouri and Texas. Grundy-swallow. False-valerian. Root strong-scented. Races differ in size of plant, size of leaves and number of heads. May-July.
Senecio pseudaureus Rydb (S. semi-cordatus Mackenzie & Bush), of the Rocky Mountain region, differing by elliptic or broadly oblong basal leaves, ranges eastward into North Dakota and Missouri.