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..
Herbs with perennial thick horizontal rootstocks, broad, basal, petioled leaves, and scaly scapes bearing racemose or corymbose heads of tubular or both tubular and radiate, white or purplish, often dioecious or subdioecious flowers. Involucre campanulate to cylindric, its bracts in 1 series, equal. Receptacle flat, or nearly so, not chaffy. Corolla of pistillate flowers very slender, 2-5-toothed, truncate or sometimes with a ray, marginal, or composing most of the head; perfect but sterile flowers with a tubular 5-cleft corolla, the style undivided. Anthers entire or minutely sagittate at the base. Fertile achenes linear, the pappus of numerous capillary rough or barbellate bristles. [Greek, a broad-rimmed hat, referring to the broad leaves of these plants.]
About 20 species, north temperate and subarctic. Type species: Tussilago Petasites L.
Flowers whitish, the pistillate radiate; natives; northern. Leaves orbicular, 7-11-cleft nearly to the base.
1. P. palmata.
Leaves deltoid-reniform, sinuate-lobed and toothed.
2. P. trigonophylla.
Leaves deltoid-ovate, repand-denticulate.
3. P. sagittata.
Flowers all rayless, purple: introduced.
4. P. Petasites.
Scape very scaly, stout, 6'-24' high. Leaves nearly orbicular in outline, 3'-12' broad, deeply 7-11-cleft to much beyond the middle, green and glabrous above, densely white-tomentose beneath, at least when young, sometimes becoming glabrate, the lobes oblong or obovate, acute, often somewhat cuneate, sharply dentate or incised; heads mostly dioecious, corymbose or racemose-corymbose, numerous, 4"-6" broad; flowers nearly white, fragrant, the marginal ones of the pistillate heads radiate.
In swamps and along streams, Newfoundland to Massachusetts, New York, Wisconsin, Minnesota and Alberta. Far western plants, formerly included in this species, prove to be distinct. April-June. Butter-bur.
Petasites trigonophylla Greene, Leaflets 1: 180. 1906.
Scape very scaly, 3'-10' high. Leaves deltoid-reniform to ovate-orbicular in outline, 2'-6' long, irregularly lobed, green and glabrous above, persistently white-tomentose beneath, the lobes few-toothed; heads corymbose, the inflorescence about 4' long; involucre campanulate; flowers nearly white, the marginal ones of the pistillate heads radiate.
Wet grounds, Quebec, Minnesota and Saskatchewan. June-Aug.
Petasites frigida (L.) Fries, admitted, in our first edition, as recorded from Lake Winnipeg, is a high boreal species, not known to occur within our area.
Tussilago sagittata Pursh, Fl. Am. Sept. 332. 1814. Nardosmia sagittata Hook. Fl. Bor. Am. 1: 307. 1833. Petasites sagittata A. Gray, in Brew. & Wats. Bot. Cal. 1: 407. 1876.
Scape and racemose-corymbose inflorescence similar to those of the two preceding species. Leaves deltoid-ovate to reniform-ovate, persistently white-tomentose beneath, glabrous or nearly so above, 4'-10' long, their margins sinuate-denticulate, neither cleft nor lobed; involucre campanulate; flowers nearly white, the marginal ones of the pistillate heads radiate.
In wet grounds, Labrador to Hudson Bay, Manitoba and Minnesota, west to British Columbia, south in the Rocky Mountains to Colorado. May-June.
Tussilago Petasites L. Sp. Pl. 866. 1753. Petasites officinalis Moench. Meth. 568. 1794. Petasites vulgaris Desf. Fl. Atlant. 2: 270. 1798. P. Petasites Karst. Deutsch. Fl. 1062. 1880-83.
Scape very scaly, 6'-15'high. Leaves orbicular or hastate-reniform, often 12' broad when mature, rounded or pointed at the apex, repand-denticulate all around, persistently white-tomentose beneath, green and mostly glabrous above; heads 4"-6" broad, mostly dioecious, in a dense raceme, the staminate ones smaller than the pistillate; flowers pink-purple, fragrant, none of them radiate.
In cultivated and waste ground, eastern Pennsylvania and Massachusetts. Naturalized from Europe. Native also of northern Asia. Batter-or flea-dock. Bog- or poison-rhubarb. Eldin. Gallon. Umbrella-leaves. Pestilence-wort. Ox-wort. April.