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..
C. trichosperma Michx. Fl. Bor. Am. 2: 139. 1803.
Coreopsis trichosperma var. tenuiloba A. Gray, Syn. Fl.
1: Part 2, 295. 1884. Bidens trichosperma tenuiloba Britton, Bull. Torr. Club 20: 281. 1893.
Annual or biennial, glabrous; stem tall, obscurely quadrangular, much branched, 2°-5° high. Lower leaves petioled, 4's' long, pinnately divided into 5-7 lanceolate or linear, acuminate, sharply serrate, incised or nearly entire, sessile or short-stalked segments; upper leaves sessile or nearly so, 3-lobed, 3-divided, or entire and linear-lanceolate; heads numerous, 11/2'-2 1/2' broad, long-peduncled; involucre hemispheric, its outer bracts linear or spatulate, sometimes ciliate, about the length of the broader inner ones; rays 6-19, obtuse, golden yellow, 7"-12" long; achenes oblong-cuneate or the inner ones narrower, hispid-pubescent and ciliate, 2"-4' long; pappus of 2 short erect or divergent, upwardly hispid teeth or short awns.
In swamps and wet meadows, Massachusetts to Georgia; Illinois to Michigan and Kentucky. Recorded from Ontario and Minnesota. Aug.-Oct.
Annual or biennial; stem much branched, 1°-3° high. Leaves thin, slender-petioled, pubescent beneath, the lower ones pinnately 5-7-divided, 3'-6' long, the segments lanceolate, serrate, incised or pinnatifid, acuminate, narrowed at the base; upper leaves less divided, lanceolate, or merely lobed, sessile or short-petioled; heads numerous, slender-peduncled, 1'-2' broad; outer bracts of the hemispheric involucre 8-10, linear or spatulate, usually ciliate, not surpassing the inner; rays 6-9, obtuse; achenes very flat, oblan-ceolate or obovate, upwardly ciliate and strigose-pubescent; pappus of 2, rarely 4, slender upwardly or downwardly barbed awns, sometimes nearly as long as the achene, rarely wanting.
In swamps and wet prairies, Ohio to Minnesota, south to Louisiana and Missouri; southeastern Pennsylvania and Delaware. Aug.-Oct.
Didens involucra a Britton, Bull. Torr. Club 20: 281. 1893.
Similar to the two preceding species, minutely pubescent, 1°-3° high, much branched. Segments of the leaves narrower, linear-lanceolate, incised or pinnatifid, long-acuminate; heads numerous, 1-2' broad, on slender usually hispid peduncles; outer bracts of the hemispheric involucre 10-20, linear-lanceolate, acuminate, densely hispid and ciliate, much exceeding the inner ones; rays orange at the base; achenes flat, ciliate and stri-gose; pappus of 2 short teeth.
In swamps,lllinois to Kansas, Arkansas and Texas; southeastern Pennsylvania and Delaware. July-Sept.