17. Euphorbia serpens Kunth (round-leaved spurge)
Chamaesyce
serpens (Kunth) Small
Map 1679, Pl.
381 k–m
Plants annual,
with taproots. Stems (2–)5–30(–40) cm long, prostrate, several- to
many-branched, the branches often overlapping (plants loosely mat-forming), not
flattened toward the tip, tan to yellowish green, sometimes slightly
pinkish-tinged, glabrous. Leaves opposite, sessile or very short-petiolate.
Stipules small scales 0.7–1.3 mm long, those from the adjacent leaf in each
pair fused into a single, small, scalelike structure on each side of the stem
positioned between the leaf bases, this often appearing irregularly fringed or
lobed. Leaf blades 2–8 mm long, oblong-ovate to broadly ovate or nearly
circular, asymmetrically rounded to shallowly cordate at the base with the side
toward the branch base usually slightly expanded into a small, rounded auricle,
rounded at the tip, the margins entire, both surfaces glabrous, the upper
surface usually light green to yellowish green, the undersurface usually pale
grayish green. Inflorescences axillary, of solitary cyathia or appearing as
small clusters on short axillary branches. Involucre 0.7–1.0 mm long, glabrous,
the rim shallowly 4-lobed or 4-toothed, the marginal glands 4, 0.3–0.6 mm long
and more or less equal in size, the body oblong to narrowly oblong, yellowish green
to green, with a relatively inconspicuous petaloid appendage 0.3–0.7 mm long,
this white to somewhat pinkish-tinged. Staminate flowers 3–8(–12) per cyathium.
Ovaries glabrous, the styles 0.2–0.4 mm long, each divided 1/8–1/2 of the way
from the tip into 2 slightly club-shaped lobes. Fruits 1.0–1.5 mm long,
glabrous. Seeds 0.9–1.2 mm long, oblong-ovate to ovate in outline, bluntly
angular in cross-section, slightly convex at the base, the surface smooth,
white to brown, lacking a caruncle. 2n=22. May–October.
Scattered, most
commonly in counties adjacent to the Missouri and Mississippi River
floodplains, but also sporadically in the Glaciated Plains and Unglaciated
Plains Divisions (U.S. [introduced in some eastern and far-western states],
Canada, Mexico, Central America, South America, Caribbean Islands). Banks of
streams and rivers, exposed margins of ponds and lakes, sloughs, oxbows, and
rarely moist depressions of glades; also ditches, margins of crop fields,
roadsides and open, disturbed areas.