13. Euphorbia missurica Raf. (prairie spurge, Missouri spurge)

Chamaesyce missurica (Raf.) Shinners

E. missurica var. intermedia (Engelm.) L.C. Wheeler

C. missurica var. calcicola Shinners

Map 1675, Pl. 381 h–j

Plants annual, with taproots. Stems 10–60 cm long, erect or ascending, several- to many-branched, the branching sometimes appearing dichotomous, not flattened toward the tip, tan to yellowish green, usually strongly pinkish- to purplish-tinged, glabrous, sometimes somewhat glaucous. Leaves opposite, sessile or very short-petiolate. Stipules small scales 0.7–1.5 mm long, those from the adjacent leaf in each pair sometimes fused toward the base on 1 or both sides of the stem into a single small structure positioned between the leaf bases, variously entire to deeply and irregularly fringed or lobed. Leaf blades (4–)8–30 mm long, linear to narrowly oblong or narrowly lanceolate-oblong, slightly asymmetrically angled or short-tapered at the base with the side toward the branch base usually slightly larger than the other side (not expanded into a distinct auricle), rounded to truncate at the tip, sometimes minutely notched or with an abrupt, minute, sharp point, the margins entire and sometimes somewhat curled under, both surfaces glabrous, the upper surface light green to bright green, the undersurface usually pale green. Inflorescences terminal at the branch tips and often also from between the branch points, of solitary cyathia or appearing as small clusters. Involucre 1.2–1.8 mm long, glabrous, the rim shallowly 4-lobed or 4-toothed, the marginal glands 4, 0.2–0.5 mm long and more or less equal in size, the body broadly oblong to nearly circular, yellowish green to green, with a relatively conspicuous petaloid appendage 0.4–2.5 mm long, this white or occasionally somewhat pinkish-tinged. Staminate flowers 24–50 per cyathium. Ovaries glabrous, the styles 0.5–1.5 mm long, each divided 1/2–3/4 of the way from the tip into 2 slender lobes. Fruits 2.0–2.5 mm long, glabrous. Seeds 1.5–2.0 mm long, more or less ovate in outline, bluntly angular in cross-section, slightly convex to nearly flat at the base, the surface smooth, inconspicuously roughened or occasionally appearing slightly wrinkled, white to brown, often somewhat mottled, lacking a caruncle. May–September.

Scattered to uncommon in the western half of the state and south of the Missouri River (Montana to New Mexico east to Minnesota and Arkansas). Glades, ledges and tops of bluffs, and margins of dry upland forest; also rarely open, disturbed areas; usually on calcareous substrates.

This attractive slender-stemmed and slender-leaved species has involucral glands with relatively conspicuous petaloid appendages. The leaves sometimes are somewhat folded longitudinally.