11. Euphorbia maculata L. (milk purslane, prostrate spurge)

Chamaesyce maculata (L.) Small

E. supina Raf.

C. supina (Raf.) Moldenke

Map 1673, Pl. 382 j–m

Plants annual, with taproots. Stems 5–45 cm long, usually prostrate, occasionally with ascending tips, several- to many-branched, the branches often overlapping (plants mat-forming), not flattened toward the tip, usually reddish brown, moderately to more commonly densely and evenly pubescent with short, appressed or incurved hairs. Leaves opposite, sessile or very short-petiolate. Stipules small scales 1.0–1.5 mm long, these not fused, often irregularly 2- or 3-lobed. Leaf blades 4–17 mm long, oblong-ovate to ovate-elliptic or oblong-elliptic, occasionally some of the leaves narrowly oblong, asymmetrical at the base with the side toward the stem tip usually angled and the other side more or less truncate and expanded into a small, rounded auricle, rounded or less commonly broadly and bluntly pointed at the tip, the margins minutely few- to several-toothed (best observed with magnification), the upper surface nearly glabrous to sparsely pubescent with relatively long, slender hairs and often also with an irregular reddish spot, the undersurface moderately to densely pubescent with somewhat appressed, sometimes somewhat woolly hairs and usually pale grayish green. Inflorescences axillary, of solitary cyathia or appearing as small clusters on short axillary branches. Involucre 0.8–1.0 mm long, sparsely hairy on the outer surface, the rim shallowly 4-lobed or 4-toothed, the marginal glands 4, 0.2–0.6 mm long and usually somewhat unequal in size, the body narrowly oblong to nearly linear, reddish purple to dark purple, with a relatively inconspicuous petaloid appendage 0.2–1.5 mm long, this white to strongly reddish-tinged. Staminate flowers 2–5 per cyathium. Ovaries hairy, the styles 0.3–0.4 mm long, each divided 1/4–1/3 of the way from the tip into 2 slightly club-shaped lobes. Fruits 1.3–1.5 mm long, sparsely to moderately and relatively evenly pubescent with appressed or strongly incurved hairs. Seeds 1.0–1.2 mm long, more or less oblong-ovate in outline, angular in cross-section, flat to slightly convex at the base, the surface with 3 or 4 low, broadly rounded cross-wrinkles, white to light brown, becoming sticky when wet, lacking a caruncle. 2n=28. May–October.

Scattered nearly throughout the state (eastern U.S. west to North Dakota and Texas; Canada; introduced farther west to Washington and California, also Hawaii, Europe, Asia). Glades, sand prairies, openings of mesic to dry upland forests, banks of streams and rivers, and receding margins of ponds, lakes, and sinkhole ponds; also crop fields, fallow fields, sidewalks, gardens, railroads, roadsides, and open, disturbed areas.

The epithet E. maculata was misapplied by most earlier botanists to plants with ascending stems that are called E. nutans in the present work. Burch (1966) reviewed the sources of data used by Linnaeus in his original descriptions of Euphorbia species and concluded that the name E. marginata was intended to apply to the prostrate-stemmed taxon. For further discussion of the distinctions between E. maculata and the closely related E. humistrata, see the treatment of that species.