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 shrubby plants, with green or partially, often more highly colored, foliage. Stems simple or branched, often irregularly so. Leaves alternate below, opposite above, similar throughout or very variable; stipules gland-like. Involucres in axillary or terminal cymes or solitary; lobes fimbriate. Glands fleshy, solitary, or rarely 3 or 4, sessile or short-stalked, without appendages, the missing ones represented by narrow lobes. Capsule exserted, the lobes rounded. Seed narrowed upward, tuberculate, without a caruncle or with a minute one only. [In honor of Joel Roberts Poinsette, of South Carolina.]
About 12 species, mostly natives of tropical America. Type species: Poinsettia pulclierrima (Willd.) Graham.
Glands of the involucre stalked; leaves nearly or quite uniform.
Leaves linear or linear-lanceolate; seeds narrowly ovoid, not prominently tuberculate.
Leaves ovate or ovate-lanceolate; seeds broadly ovoid, prominently tuberculate.
Glands of the involucre sessile; leaves various.
Euphorbia dentata var. cuphosperma Engelm. Bot. Mex. Bound. Surv. 190. 1859.
Poinsettia cuphosperma Small, Fl. SE. U. S. 721. 1903.
Annual, usually sparingly pubescent. Stem erect, slender, simple, or sparingly branched, 8-15' high. Leaves opposite or alternate, linear, oblong, or linear-lanceolate, 10"-3' long, entire, undulate, or denticulate, narrowed into a slender petiole; involucres crowded at the ends of the branches, nearly sessile, glabrous, or nearly so, nearly 2" long, bearing about 4 long-stalked unappendaged glands; capsule glabrous, or sparingly pubescent, 2\" in diameter, seeds narrowly ovoid, about 1 1/2" long, irregularly 4-angled, ridged and slightly tuberculate.
South Dakota to Colorado and Mexico Aug-Sept.
Euphorbia dentata Michx Fl. Bor. Am. 2: 211. 1803. Poinsettia dentata Small, Fl. SE. U. S. 722. 1903.
Annual, dull green, pubescent. Stem erect or ascending, 8-15' high, somewhat woody below, branched, the branches mostly ascending; leaves opposite, or the lowest alternate, varying from ovate to nearly linear or orbicular-oblong, 5"-3 1/2' long, coarsely dentate, narrowed into slender petioles, the nerves prominent beneath; involucres clustered at the ends of the branches, oblong-campanulate, about 1 1/2" long, 3-5-lobed, bearing 1-4 yellowish short-stalked glands without appendages; capsule glabrous, 2"-2 1/2" in diameter; seeds ovoid or ovoid-globose, ash-colored, irregularly tuberculate, inconspicuously 4-angled.
In dry or moist soil, Pennsylvania to South Dakota, Wyoming, Tennessee, Louisiana and Mexico. July-Oct.
Euphorbia heterophylla L. Sp. PL 453. 1753. P. heterophylla Kl. & Garcke, Monatsb. Akad.
Berlin 1859: 253- Annual or biennial, bright green, pubescent or nearly glabrous. Stem mostly erect, 1°-3° tall, woody below, with the branches ascending, or the lower spreading, leafy at the ends; leaves alternate, very variable, linear to orbicular, entire, undulate, sinuate or dentate, the uppermost often fiddle-shaped and blotched with red; all slender-petioled; involucres clustered at the ends of branches, \\" long, about equalling the peduncles; cleft into 5 ovate or oblong laciniate lobes, the sinuses bearing 1 or several sessile glands without appendages; capsule glabrous or minutely pubescent, 3" in diameter; seeds oblong-ovoid, 1 1/2" long, transversely wrinkled and tuberculate.
Illinois to South Dakota, Florida, Kansas and Texas. Tropical America. April-Nov.