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..
Annual or perennial herbs, or shrubs. Stems often radially branched at the base, the branches ascending or prostrate, sometimes creeping, forking. Leaves opposite, entire or toothed, more or less oblique at the base; stipules delicate, entire or fringed. Involucres solitary in the axils or in axillary cymes; glands 4, sessile or stalked, naked or usually with an appendage, one sinus of each involucre glandless. Capsule smooth, sometimes pubescent, the angles sharp or rounded. Seeds angled, with minute caruncles, white or black, the faces smooth or transversely wrinkled. [Greek, ground-fig.]
About 225 species, widely distributed in temperate and tropical regions. Type species: Chamaesyce maritima S. F. Gray.
This genus and the following ones of the family were all included in Euphorbia in our first edition, but the true Euphorbias are African, nearly or quite leafless tall and stout plants, very different from any of ours.
‡ Leaves entire; seeds smooth.
Plants branched at the base, the branches prostrate.
Seeds 1 1/2" long.
Seeds 1/2"-3/4" long.
Leaves usually more than twice as long as broad; seeds nearly terete, 3/4" long.
Leaves usually less than twice as long as broad; seeds obtusely 4-angled, 1/2" long.
Plants with an erect or ascending stem, branched above, branches ascending.
Seeds nearly terete, 1" long; leaves usually flat and straight.
Seeds 4-angled, 3/4" long; leaves often involute and curved.
XX Leaves entire; seeds variously roughened.
‡‡‡ Leaves serrate or dentate; plants prostrate or spreading.
Seeds faintly transversely ridged and pitted.
Seeds brown, about 1/2" long; leaves broad.
Seeds gray, about 3/4" long; leaves narrow.
Seeds strongly transversely ridged, not pitted.
Herbage pubescent, or puberulent.
Seeds narrow, fully 1/2" long, fully twice as long as wide, the faces pitted.
Seeds broad, less than 1/2" long, less than twice as long as wide, the faces wrinkled.
Leaves broad; involucre deeply split on one side; seeds blunt-angled.
Leaves narrow; involucre not deeply split; seeds sharp-angled.
‡‡‡‡ Leaves serrate or dentate; plants erect or ascending.