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 more or less woolly, with opposite leaves, and small corymbose heads, of both tubular and radiate yellow flowers. Involucre campanulate or hemispheric, its bracts in 1 or 2 series, herbaceous, obtuse, appressed, nearly equal. Receptacle small, nearly flat, naked, foveolate. Ray-flowers in 1 series, pistillate, fertile. Disk-flowers perfect, fertile, their corollas with campanulate or cylindric, 5-cleft limb. Anthers entire or emarginate at the base. Style-tips mostly truncate and obtuse. Achenes quadrangular, linear or oblong. Pappus of several scales, obtuse or truncate and scarious at the apex. [Named for its resemblance to Picradenia.] Two known species, natives of western North America, the following typical.
Trichophyllum oppositifolium Nutt. Gen. 2: 167. 1818.
Bahia oppositifolium Nutt.; T. & G. Fl. N. A. 2: 376. 1842.
P. oppositifolia Rydb.; Britton, Manual 1008. 1901.
Perennial, herbaceous; stem densely cinereous, much branched, 4'-12' high, very leafy. Leaves opposite, or the uppermost alternate, 1/2' - 1 1/2' long, palmately 2-5-parted into linear, obtuse or obtusish, entire segments, finely cinereous on both sides; heads short-peduncled, 6"- 9" broad; involucre campanulate, or becoming hemispheric, its bracts oblong, obtuse, densely tomentose; rays 5-7, short; achenes linear-oblong, glandular-pubescent; pappus of 4-8 spatulate to lanceolate scales with thickened bases.
On plains, especially in alkaline soil, South Dakota to Montana, Nebraska, Texas, New Mexico. June-Sept.