18. Ranunculus sardous Crantz (hairy buttercup)

Pl. 517 a–c; Map 2384

Plants annuals. Roots not tuberous. Stems 5–50 cm long, erect or ascending, not rooting at the lower nodes, moderately to densely (rarely sparsely) pubescent with more or less spreading hairs, without bulbils, the base not bulbous. Basal leaves usually present at flowering (sometimes withered at fruiting), long-petiolate, the blade 1–7 cm long, 1–6 cm wide, ovate to more or less heart-shaped in outline, usually compound (rarely only deeply divided), with 3 leaflets (or lobes), the base rounded to cordate, the terminal leaflet often short-stalked, the primary leaflets (or lobes) usually again 2– or 3-lobed, the segments oblong to obovate or rhombic, the margins otherwise coarsely toothed, the teeth mostly rounded to bluntly pointed at their tips. Stem leaves mostly short-petiolate to sessile, progressively reduced toward the stem tip, the blade progressively deeply 3-parted into narrower, less divided and toothed, more sharply pointed segments, those of the uppermost leaves linear to narrowly oblong-oblanceolate. Sepals 5, 3–6 mm long, reflexed from ca. 1–3 mm above the base along a well-defined transverse fold, more or less plane (the apical portion sometimes appearing somewhat folded longitudinally). Petals 5, 7–10 mm long, 4–8 mm wide, obovate to broadly oblong-obovate, longer than the sepals, yellow. Style present. Head of achenes 5–8 mm long at maturity, globose to ovoid, the receptacle hairy. Achenes 2–3 mm long, the dorsal margin keeled and narrowly winged, the wall thick, usually pebbled or with minute papillae, occasionally smooth, glabrous, the beak 0.4–0.7 mm long, flattened, oblong to triangular, curved. 2n=16. April–June, rarely July–October.

Introduced, scattered in the Mississippi Lowlands, Ozark, and Ozark Border Divisions and sporadic in the Glaciated Plains (native of Europe, Asia; introduced in the eastern U.S. west to Oklahoma and Texas, also in the western U.S. from Washington to California; Canada, Australia, Pacific Islands). Banks of streams and rivers, sloughs, acid seeps, margins of sinkhole ponds, and openings of bottomland forests; also ditches, levees, pastures, fallow fields, edges of crop fields, farm yards, railroads, roadsides, and open, disturbed areas.

Steyermark (1963) knew R. sardous from Missouri based only on a single historical specimen from St. Louis County, but commented that it was then already relatively common in adjacent portions of southern Illinois. It has spread dramatically in southern Missouri since the 1960s. This species is avoided by cattle and can become quite dense and showy in heavily grazed pastures.