This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", 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 (in our species) mostly 3-foliolate, denticulate leaves, and purple pink red white or yellow flowers in dense heads or spikes. Stipules adnate to the petiole. Calyx-teeth nearly equal. Petals commonly persistent, their claws more or less completely adnate to the stamen-tube. Stamens diadelphous, or the tenth one separate for only a portion of its length. Ovary sessile or stipitate, few-ovuled. Pod oblong or terete, often included in the calyx, membranous, indehiscent or tardily dehiscent by 1 suture, or by a lid, 1-6-seeded. [Latin, referring to the 3 leaflets.]
About 275 species, most abundant in the north temperate zone, a few in South America and South Africa. Besides the following, about 60 others occur in the western part of the continent. Type species: Trifolium pratense L.
Flowers yellow. [Genus Chrysaspis Desv.]
Head 6"-9" long; stipules linear; leaflets all sessile.
Head 4"-6" long, nearly globose; stipules ovate; terminal leaflet stalked.
Head 20-40-flowered; standard conspicuously striate.
Head 10-12-flowered; standard scarcely striate.
Flowers red, purple, or white.
Head or spike much longer than thick; calyx silky, its teeth plumose.
Corolla crimson, equalling or exceeding the calyx-lobes.
Corolla whitish, shorter than the calyx-lobes.
Head globose, oval or ovoid.
Flowers sessile, or very nearly so; heads dense, ovoid, oval or globose.
Heads mostly sessile, or nearly so; calyx pubescent.
Heads always distinctly peduncled.
Plant glabrous throughout.
Flowers pedicelled; heads umbel-like, globose.
Heads 1' in diameter or more; peduncles 1'-3' long.
Prostrate; pubescent; perennial.
Ascending; pubescent; annual or biennial.
Stoloniferous; glabrous; perennial.
Heads 6"-9" in diameter; lower peduncles 2'-8' long.
Ascending or procumbent; flowers pink, pinkish, or purple.
Ascending; calyx much shorter than the pink or nearly white corolla.
Procumbent; tufted; calyx nearly equalling the purple corolla.
Creeping; flowers white or pinkish.