1. Stylophorum diphyllum (Michx.) Nutt. (celandine poppy, wood poppy)

Pl. 476 h, i; Map 2179

Plants perennial herbs, with thick, sometimes branched rhizomes; sap yellow to yellowish orange. Aerial stems 30–50 cm long, sometimes branched, loosely to strongly ascending, often purplish-tinged at the base, moderately to densely pubescent with fine, more or less spreading, multicellular hairs. Leaves with the upper surface green, glabrous, the undersurface pale and glaucous, sparsely hairy; basal leaves several, 30–50 cm long, long-petiolate (the petiole often purplish-tinged at the base), the blade pinnately deeply lobed or compound into 5 or 7 lobes or leaflets, these oblong-obovate, rounded at the tip, the margins irregularly scalloped and/or bluntly toothed, sometimes also shallowly few-lobed; stem leaves 2, subopposite, similar to the basal leaves, but somewhat smaller and usually short-petiolate. Inflorescences terminal, umbellate, the umbel sessile, few-flowered, sometimes reduced to a solitary flower, the individual flower stalks 2–5 cm long, ascending, hairy, slightly expanded at the tip but not forming a cup or disc, each with a bract at the base, this 3–5 mm long, narrowly oblong-elliptic, hairy along the entire margins and usually also sparsely so on the undersurface. Sepals 2, free, shed individually as the flower opens, 12–15 mm long, broadly elliptic-ovate and deeply concave (cupped around the flower), broadly pointed at the tip. Petals 4, 20–30 mm long and wide, broadly obovate, rounded at the tip, yellow. Stamens numerous. Ovary tapered to a persistent style 3–6 mm long, the stigma more or less capitate, with 3 or 4(5), shallow, spreading lobes. Fruits 20–30 mm long, nodding, ellipsoid, moderately to densely pubescent with relatively stout, bristly, multicellular hairs, dehiscing longitudinally from the tip by 4(5) valves. Seeds 1.6–2.1 mm long, ovoid, with a crestlike aril along 1 side, the surface otherwise with a network of fine ridges and pits, light brown to brown, not shiny. 2n=20. April–June.

Scattered to common in the eastern half of the Ozark and Ozark Border Divisions, less common elsewhere in the Ozarks and the Big Rivers, apparently absent from most of the Glaciated Plains, Unglaciated Plains, and Mississippi Lowlands Divisions (Missouri to Michigan and Ohio south to Arkansas, Alabama, Georgia, and Virginia; Canada). Bottomland forests, mesic upland forests, banks of streams and rivers, and bases and ledges of bluffs.

This attractive wildflower has become popular in native shade gardens. However, it can spread aggressively by seed in suitable habitats. Vegetatively, it can be very difficult to distinguish from Chelidonium majus.