6. Euphorbia dentata Michx. (toothed spurge)

Poinsettia dentata (Michx.) Klotzsch & Garcke

E. dentata var. linearis Engelm. ex Boiss.

E. cruentata Graham

Map 1668, Pl. 379 i, j

Plants annual, with taproots. Stems 15–60 cm long, erect or ascending, unbranched or few- to several-branched, the branches not flattened toward the tip, usually green to yellowish green, occasionally reddish- to purplish-tinged, densely pubescent with minute, downward-curved or downward-angled hairs, usually also with scattered, longer, multicellular hairs. Leaves opposite (occasionally alternate at 1 or 2 of the uppermost nodes), short- to long-petiolate. Stipules absent or a pair of minute, light brown, convex, sessile glands. Leaf blades 10–60 mm long, highly variable in shape, linear to lanceolate, elliptic, ovate, or nearly circular, not lobed, more or less symmetrically rounded to angled or tapered at the base, rounded or angled to tapered to a usually bluntly pointed tip, the margins relatively coarsely and often irregularly toothed or less commonly finely toothed to scalloped, wavy, or nearly entire, the surfaces sparsely to densely pubescent or occasionally nearly glabrous, green to dull grayish green and sometimes reddish- to purplish-tinged toward the margins or base, the undersurface with somewhat longer, relatively slender hairs (these not expanded at the base) and paler green than the upper surface. Inflorescences terminal, often a small, umbellate panicle with a whorl of leaves at the base, but this frequently reduced to 1–3 small clusters of cyathia. Involucre 2.5–3.5 mm long, glabrous, the rim irregularly lobed and fringed, the marginal glands 1 or more commonly 2, 0.7–1.2 mm long, appearing strongly concave and more or less 2-lipped, yellowish green to yellowish brown, lacking a petaloid appendage. Staminate flowers 25–40 per cyathium. Ovaries glabrous, the styles 1.0–1.5 mm long, each divided 1/2–2/3 of the way from the tip into 2 slightly club-shaped lobes. Fruits 3–5 mm long (somewhat broader), glabrous. Seeds 2.5–3.0 mm long, ovate to broadly ovate in outline, more or less rounded in cross-section (the oblique apical portion surrounding the caruncle angled but the longitudinal inner faces appearing rounded), more or less flattened to slightly concave at the base, the surface appearing relatively finely warty or with fine, relatively evenly spaced tubercles, light gray to dark brown or nearly black, often appearing somewhat mottled, often with a small but well-developed, pale caruncle. 2n=28. July–October.

Scattered nearly throughout the state (Texas to Georgia north to Nebraska and Pennsylvania; Mexico; introduced elsewhere in the U.S.). Banks of streams and rivers, ledges and tops of bluffs, bottomland forests, mesic to dry upland forests, glades, and upland prairies; also crop fields, fallow fields, old fields, gardens, ditches, railroads, roadsides, and open, disturbed areas.

Steyermark (1963) referred two historical collections from Barton and Jackson Counties to E. cuphosperma (Engelm.) Boiss. (as E. dentata f. cuphosperma (Engelm.) Fernald; also known as E. dentata var. cuphosperma Engelm., Poinsettia dentata var. cuphosperma (Engelm.) Mohl.), based on their linear to narrowly lanceolate leaves. That taxon, which occurs from Arizona and New Mexico south through Mexico to Central America, is differentiated from all of the Missouri materials in the complex by its hairy (vs. glabrous) ovaries and fruits, and by its cyathia with relatively elongate involucral glands tapered to a stalklike base. Steyermark misapplied this name to Missouri specimens and the taxon is here excluded from the Missouri flora. The two specimens in question correspond better to var. linearis, a narrow-leaved form of E. dentata unworthy of formal taxonomic recognition that was first described from near St. Louis in adjacent western Illinois.