1. Hydrocotyle ranunculoides L.f. (buttercup pennywort)

Map 863

Leaf blades 1.0–5.5 cm wide, deeply cordate at the base, broadly depressed-oval to more commonly broadly kidney-shaped, the margins finely scalloped and 2–4-lobed up to half the way to the base. Inflorescences of simple umbels of 4–10 flowers, these short-stalked. Fruits 1–3 mm long, circular to depressed-circular in outline, rounded or truncate to rarely very shallowly cordate at the base and tip, each mericarp with the ribs all inconspicuous and not thickened. 2n=24. May–August.

Possibly introduced, known thus far only from a single specimen from Stoddard County (eastern U.S. west to Kansas and Texas, also Washington, Oregon, California, and Arizona; Canada, Mexico, Central America, South America). Emergent aquatic along the margin of a slough.

This species was first discovered in the state by Stan Hudson in 2000. It is known to occur in adjacent states, including Arkansas, Illinois, Kansas, Oklahoma, and Tennessee, and was thus to be expected in Missouri. However, the population in Stoddard County grows near an office building and former homesite. Thus, it is unclear whether the species is a native component of the aquatic plant community at the site or whether it escaped from historical cultivation in the vicinity.