4. Hibiscus trionum L. (flower-of-an-hour, Venice mallow)

Pl. 453 c, d; Map 2054

Plants annual. Stems 25–55 cm long, mostly spreading to loosely ascending, moderately to densely hairy when young, becoming glabrous or nearly so with age. Leaf blades 1–6 cm long, broadly ovate in outline, deeply 3-lobed (often appearing nearly compound), the main lobes often shallowly to deeply lobed again, the margins coarsely scalloped or bluntly toothed, the upper surface sparsely pubescent with simple and/or fasciculate hairs along the veins, the undersurface moderately pubescent with stellate and fasciculate hairs. Stipules persistent. Bractlets subtending the calyx 10–12(–15), 4–10 mm long, bristly pubescent especially along the margins with simple or fasciculate hairs. Calyces 9–12 mm long at flowering, becoming greatly enlarged to 16–22 mm, papery, and inflated at fruiting, the main veins raised and ridgelike, dark green to dark purple, bristly pubescent with simple or fasciculate hairs. Petals 1.5–4.0 cm long, cream-colored to yellow with dark reddish purple bases. Fruits 0.9–1.6 cm long, ovoid-cylindric to nearly globose, hairy. Seeds 5–8 per locule, 2.0–2.5 mm long, broadly kidney-shaped to nearly, triangular in outline, the surface minutely warty and usually also with minute stellate hairs, dark brown or grayish black. 2n=28, 56. June–September.

Introduced, scattered to common nearly throughout the state, although apparently still absent from the Mississippi Lowlands Division (native of Europe, widely introduced in North America). Margins of ponds and lakes and banks of streams and rivers; also crop fields, fallow fields, gardens, roadsides, railroads, and open disturbed areas.

This species originally was introduced into the United States as a garden ornamental, but has become a problem weed of horticultural crops. Several cultivars are still grown as annual bedding plants for their beautiful flowers.