This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Petasites palmatus, Gray Native. Perennial. Propagates by seeds and by rootstocks.
Time of bloom: April to June.
Seed-time: May to July.
Range: Newfoundland to British Columbia and Alaska, southward to Massachusetts, New York, Michigan, and Minnesota. Habitat: Recently cleared ground, wet meadows, and swamps.
Scapes stout, appearing before the leaves, very scaly, and varying in height from about six inches when in first bloom to nearly two feet when mature. Heads in corymbose terminal clusters, each less than a half-inch broad, pale yellow or cream-color, and fragrant; they are partly dioecious, the fertile plants having heads almost wholly pistillate, with one or more outer rows of ray florets; the perfect but sterile flowers have tubular five-cleft corollas with undivided styles. Leaves finally very large, often more than a foot broad, rounded, palmately and very deeply lobed, with five to seven segments also cut and toothed, glossy and deep green above but densely white-woolly below especially when young. Rootstocks very large and thick.
Like Tussilago, this weed is driven out by drainage and cultivation.