1. Euphorbia commutata Engelm. ex A. Gray (wood spurge)

Tithymalus commutatus (Engelm. ex A. Gray) Klotzsch & Garcke

E. commutata var. erecta Norton

Map 1663, Pl. 380 c–e

Plants perennial herbs, with fibrous roots. Stems 10–40 cm long, ascending from a frequently spreading base, often branched from near the base (spreading to loosely ascending overwintering shoots often produced in the late summer and autumn, these producing new growth the following spring), otherwise often unbranched below the inflorescence, the branches not flattened toward the tip, green to yellowish green, usually strongly reddish- or purplish-tinged especially toward the base, glabrous. Leaves alternate above the lowermost node and below the inflorescence branches (those of the inflorescence branches opposite) not appearing crowded, sessile or rarely minutely petiolate (those of the overwintering shoots mostly short-petiolate). Stipules absent. Leaf blades 5–30 mm long, unlobed, the margins entire, the surfaces glabrous, green to yellowish green, especially those of the lower leaves often strongly reddish- or purplish-tinged; those below the inflorescence oblanceolate to obovate, tapered at the base, rounded or abruptly short-tapered to a minute, sharply pointed tip; those along the inflorescence branches kidney-shaped to broadly triangular-ovate or broadly ovate (slightly longer than wide to somewhat wider than long), broadly rounded to cordate and clasping the stem or occasionally perfoliate, the terminal ones somewhat cupped around the cyathia, rounded or very broadly angled to a bluntly pointed tip. Inflorescences terminal, often umbellate panicles with opposite or whorled leaves at the base and each of the (2)3(4) primary branches usually branched 1–3 additional times, the cyathia solitary at the branch points and solitary or more commonly in small clusters at the branch tips. Involucre 1.7–2.5 mm long, glabrous, the rim shallowly 4-lobed, the margin usually minutely and inconspicuously hairy, the marginal glands 4, 0.8–1.3 mm long, more or less crescent, the oblong body tapered into a pair of slender, spreading horns, yellow, lacking petaloid appendages. Staminate flowers 9–15 per cyathium. Ovaries glabrous, the styles 0.9–1.3 mm long, each divided 1/2–2/3 of the way from the tip into 2 relatively slender lobes. Fruits 2.7–3.5 mm long, glabrous, smooth. Seeds 1.5–2.0 mm long, broadly oblong-elliptic to broadly ovate or nearly circular in outline, nearly circular in cross-section, rounded or slightly angled at the base, the surface strongly pitted, dull gray to olive gray, with a pale, irregularly winglike caruncle (shaped similar to a tiny fortune cookie). 2n=28. April–June.

Scattered in the Ozark and Ozark Border Divisions (eastern U.S. to Iowa and Texas; Canada). Bottomland forests, mesic to dry upland forests, bases and ledges of bluffs, banks of streams and rivers, edges of glades, and rarely edges of fens.

This dainty species is relatively uniform in its morphology across its range. Some plants from the southeastern portion of the range (northward into Missouri) tend to have more persistent leaves on the overwintering shoots. They have been called var. erecta, but this variant is not sufficiently distinct to warrant recognition. However, some populations occurring from the Ouachita Mountains of eastern Oklahoma and adjacent west-central Arkansas northward to Barry County, Missouri, may represent an undescribed cryptic taxon. These plants, which currently are under study by Mark Mayfield of Kansas State University, differ from typical E. commutata in their more delicate habit and smaller, more deeply pitted, more oblong seeds. True E. commutata also tends to produce overwintering vegetative growth with distinctly petiolate oblanceolate leaves that commonly wither in the middle of spring, leaving a set of closely spaced leaf scars at the base (this phenomenon apparently is absent in the other taxon).