3. Euphorbia cyathophora Murray (painted leaf, fire-on-the-mountain)

Poinsettia cyathophora (Murray) Klotzsch & Garcke

P. cyathophora var. graminifolia (Michx.) Mohl.

E. heterophylla L. var. graminifolia (Michx.) Engelm.

Map 1665, Pl. 379 c–e

Plants annual, with taproots. Stems 15–100 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, glabrous or with sparse multicellular hairs around the nodes. Leaves alternate above the lowest node and below the inflorescence branches (those of the lowermost node and the inflorescence branches usually opposite), mostly short-petiolate. Stipules absent or a pair of minute, light brown, convex, sessile glands. Leaf blades 15–150 mm long, highly variable in shape, linear to lanceolate, elliptic, ovate, or broadly elliptic, those of the upper leaves sometimes pinnately few-lobed (more or less fiddle-shaped), more or less symmetrically angled or tapered at the base, rounded or angled to tapered to a sharply pointed tip, the margins entire or toothed, the upper surface glabrous, bright green and (on the uppermost leaves) sometimes with a bright red to reddish purple (rarely pink, yellow, or white) region toward the base, the undersurface glabrous or sparsely pubescent with relatively stout, multicellular hairs, light green to pale green. Inflorescences terminal at the branch tips (not an umbellate panicle with a whorl of leaves at the base), of solitary or more commonly paired cyathia, sometimes appearing as small clusters. Involucre 2.0–2.5 mm long, glabrous, the rim irregularly lobed and fringed, the marginal glands 1 or less commonly 2, 0.7–1.5 mm long, appearing strongly concave and more or less 2-lipped, yellowish green to yellowish brown, lacking a petaloid appendage. Staminate flowers 30–50 per cyathium. Ovaries glabrous, the styles 0.8–1.1 mm long, each divided 1/2–2/3 of the way from the tip into 2 slightly club-shaped lobes. Fruits 3–4 mm long (nearly twice as broad), glabrous. Seeds 2.5–3.0 mm long, ovate to oblong-ovate in outline, more or less circular in cross-section, more or less flattened to slightly concave at the base, the surface with a network of low, sharp ridges or wrinkles and low, pointed tubercles, dark brown with the tips of the ridges and tubercles lighter brown, usually lacking a caruncle, a minute, discolored, slightly raised area occasionally present. 2n=28, 56. July–October.

Scattered mostly south of the Missouri River (California to Florida north to Utah, South Dakota, Ohio, and Maryland [introduced in much of the western and northern portions of the range]; Mexico, Central America, South America, Caribbean Islands; introduced in Hawaii, Asia). Banks of streams and rivers, bases of bluffs, and bottomland forests; also fallow fields, old fields, gardens, roadsides, and open, disturbed areas.

This species was long-known to midwestern botanists by the name E. heterophylla (Poinsettia heterophylla (L.) Klotzsch & Garcke). Dressler (1961) noted that true E. heterophylla is a different (Neotropical) species and that temperate North American plants are properly known as E. cyathophora. Botanists who have studied E. cyathophora have all remarked upon the extreme morphological plasticity within individual plants for characters such as leaf shape and coloration. Steyermark (1963) did not know the species from the Mississippi Lowlands Division, but it has become increasingly common in southern Missouri over the last few decades.