9. Ranunculus flabellaris Raf. (yellow water crowfoot)

R. flabellaris f. riparius Fernald

Pl. 518 a; Map 2375

Plants perennials. Roots not tuberous. Stems mostly 30–70 cm long, shorter when terrestrial, weak (usually submerged in water, when stranded on mud then appearing prostrate), usually rooting at the lower nodes, glabrous or somewhat hairy (when terrestrial), without bulbils, the base not bulbous-thickened, but the stem sometimes appearing somewhat inflated above the base (when aquatic). Basal leaves absent at flowering when aquatic or sometimes present when terrestrial. Leaves mostly long-petiolate toward the stem base, short-petiolate to sessile near the tip, the blade 1.2–7.5 cm long, 1.5–11.0 cm wide, broadly fan-shaped to semicircular or kidney-shaped in outline; those of the submerged leaves 2–5 times pinnately, ternately, and occasionally partially dichotomously dissected into threadlike or linear flattened, mostly sharply pointed segments 0.2–2.0 mm wide; grading into those of emergent or terrestrial leaves, which are less divided, mostly ternately compound or deeply divided (the smaller leaves occasionally merely 3-lobed), truncate to deeply cordate at the base, the leaflets or segments variously undivided or 1 or 2 times shallowly to deeply lobed, variously rhombic to nearly circular, the ultimate segments rounded to sharply pointed at the tip, the margins otherwise entire or sharply few-toothed. Sepals 5, 5–8 mm long, spreading or slightly recurved, plane. Petals 5(6–14), 7–12 mm long, 5–9 mm wide, obovate, noticeably longer than the sepals, yellow. Style present. Head of achenes 7–12 mm long at maturity, ovoid to globose, the receptacle sparsely hairy. Achenes 1.8–2.2 mm long, the margins corky-thickened, especially toward the achene base, the wall thick, smooth, glabrous, the beak 1.0–1.8 mm long, flattened, lanceolate, straight. 2n=32. April–July.

Scattered in the southeastern quarter of the state and uncommon to scattered in the northern half of the state, mostly in counties along the Missouri and Mississippi Rivers (nearly throughout the U.S. [except for some southern states]; Canada). Streams, rivers, spring branches, oxbows, swamps, ponds, lakes, sinkhole ponds, sloughs, and marshes; submerged aquatics, emergent in shallow water, or terrestrial in wet soils.

Terrestrial plants of R. flabellaris are similar in appearance to those of R. sceleratus, a taxon that is usually terrestrial but occasionally occurs in shallow water. Specimens of that species differ in their erect stems, shorter petals (2–5 mm) and nearly beakless achenes.

Ranunculus flabellaris was used medicinally by Native Americans to treat colds and respiratory ailments (Moerman, 1998).