1. Oxalis corniculata L. (creeping wood sorrel)

O. corniculata var. atropurpurea Planch.

O. repens Thunb.

Pl. 474 e-g; Map 2166

Plants perennial, but flowering the first year and sometimes appearing annual, with small taproots, lacking bulbs. Aerial stems commonly 2 to several from the rootstock, 4–10(–25) cm long, the main stems green or darkened and creeping (sometimes with ascending branches), stoloniferous, rooting at all or most of the nodes, sparsely pubescent with mostly appressed hairs (the ascending branches usually more densely hairy). Leaves basal (on young plants) and alternate, those on older stems often appearing fasciculate from the stem nodes, the petiole moderately to densely pubescent with appressed to strongly ascending hairs. Stipules represented by a pair of small (1.5–2.5 mm), oblong, rounded to truncate auricles at the petiole base, these usually brown. Leaflets 4–12 mm long, obcordate, the apical notch to 1/3 of the total length, the upper surface glabrous or sparsely pubescent with short, curved to loosely appressed hairs, the undersurface moderately to densely pubescent with mostly appressed hairs, green or the surfaces or margins purplish- to brownish-tinged. Inflorescences umbellate with 2 or 3(–6) flowers, occasionally reduced to a solitary flower. Sepals 2.5–5.0 mm long, oblong-lanceolate to narrowly ovate, green or translucent at the tip. Petals 4–8 mm long, yellow. Fruits 7–20 mm long, cylindrical at maturity, sparsely pubescent with short, curled or curved, unicellular hairs or sometimes glabrous. Seeds 1.0–1.8 mm long, brown, the ridges not whitened. 2n=24, 36, 42, 46, 48. April–November.

Introduced, uncommon and widely scattered, mostly in and around urban areas (native range poorly known but possibly the Old World tropics, presently known nearly worldwide). Banks of streams and rivers, margins of ponds, lakes, and sinkhole ponds, and occasionally disturbed openings of bottomland and mesic upland forests; also pastures, fallow fields, greenouses, gardens, lawns, roadsides, and open disturbed areas.

Opinions have varied on the origin of this cosmopolitan weed. K. R. Robertson (1975) and some other authors considered it to be native to portions of the Old World, Eiten (1963) and Lourteig (1979) both suggested that the species is native in both the Old and New Worlds, including potentially at least the southeastern United States. However, authors of regional floristic treatments, even for states such as Florida (D. B. Ward, 2004) mostly have considered the species introduced in their regions, based on its discontinuous occurrences and restriction to disturbed habitats.

B. L. Turner (1994) applied the name O. corniculata var. wrightii (A. Gray) B.L. Turner to plants from the central portion of the United States (including Missouri), but that name applies to a western species that Eiten (1963) called O. albicans Kunth. Turner’s concept of the taxon appears to be an amalgamation of plants here called O. dillenii and O. stricta.