1. Staphylea trifolia L. (American bladdernut)

Pl. 568 d–f; Map 2650

Plants shrubs or rarely small trees to 3 m tall, colonial by root suckers. Bark smooth or slightly furrowed with age, often appearing somewhat striped on branches, sometimes peeling in fine flakes with age. Twigs not angled, glabrous or minutely and inconspicuously hairy, greenish brown to reddish brown, the buds lateral, with several scales, ovate in outline, reddish brown, glabrous. Leaves opposite, long-petiolate. Stipules inconspicuous, membranous, linear, shed as the leaves develop. Leaf blades trifoliate, the lateral leaflets short-stalked to nearly sessile, the middle leaflet longer-stalked. Leaflets 4–10 cm long, ovate to elliptic or oblong-obovate, short-tapered to a sharply pointed tip, narrowed or tapered at the base (the lateral ones sometimes asymmetric at the base), the margins finely toothed, the upper surface glabrous at maturity or sparsely pubescent with shorter hairs, the undersurface moderately to densely pubescent with longer, crinkled, mostly multicellular hairs. Inflorescences axillary or terminal on second year’s branch growth, loose racemelike clusters 4–10 cm long, pendant, produced as the leaves develop or afterward. Flowers perfect, hypogynous, actinomorphic. Calyx of 5 sepals, these fused at the base, 6–8 mm long, oblong-ovate to oblong-triangular, erect, green, glabrous. Corolla of 5 petals, these 8–10 mm long, obovate, erect with a usually spreading tip, white to greenish white. Stamens 5, small, free, the filaments attached at the base of a nectar disc, hairy below the midpoint, the anthers attached at the notch of the cordate base, exserted, yellow. Pistil 1 per flower, of 3 fused carpels. Ovary superior, 3 lobed, 3-locular, the placentation axile or appearing basal, with 4–12 ovules per locule. Styles 3, fused toward the base and also at the very tip, the stigmas forming a more or less disc-shaped mass. Fruits strongly inflated pendant capsules, 3–5 cm long, obovoid, 3-lobed at maturity toward the tip, the lobes narrowed to sharply pointed tips, the walls thin and papery to somewhat leathery, brown, indehiscent or eventually dehiscent from the tip along the inner sutures of the lobes, usually persistent through the winter. Seeds 1–4 per locule, 5.5–6.0 cm long, ellipsoid to nearly globose, slightly flattened, the surface smooth, brown, somewhat shiny. 2n=78. April–May.

Scattered to common throughout the state (eastern U.S. west to Minnesota, Nebraska, and Oklahoma; Canada). Banks of streams and rivers, bases and sheltered ledges of bluffs, and mesic upland forests in ravines, often on north- to east-facing slopes on calcareous substrates.

Bladdernut is sometimes cultivated as an ornamental shrub for its unusual fruits and attractive flowers. The leaves remain green until late in autumn, eventually turning yellowish green. It is easily distinguished vegetatively from the superficially similar Ptelea trifoliata L. (Rutaceae, hop tree) by its opposite leaves with a relatively long-stalked central leaflet.