Wisteria Nutt. (wisteria)

Plants lianas (rarely shrubs elsewhere), often with rhizomes. Stems to 15 m or more long, high-climbing, strongly woody, stout, twining, unarmed, glabrous or nearly so, the bark relatively thin, initially smooth but developing a fine network of lines, furrows, or wrinkles, tan to brown, with conspicuous elongate, transverse lenticels, these becoming obscured with age. Leaves odd-pinnately compound, petiolate, with 7–13 leaflets. Stipules 1–3 mm long, linear, shed early; stipels similar to the stipules, mostly shed early. Leaflets ovate to elliptic, rounded to broadly angled at the base, tapered to a usually sharply pointed tip, the margins entire, the surfaces variously glabrous or hairy, the venation pinnate, the terminal leaflet with the stalk 10–25 mm long, the lateral leaflets very short-stalked. Inflorescences terminal racemes, showy and with usually numerous flowers, drooping or pendant, appearing before the leaves or as the leaves develop, the stalk usually short (less than 15 mm long), but often appearing longer if the lower flowers abort and are shed, the bracts 4–14 mm long, lanceolate, shed early; bractlets absent. Calyces 2-lipped, hairy, sometimes also with club-shaped, stalked glands, the tube shorter than to longer than the lobes, more or less bell-shaped, the upper lip slightly shorter than the lower lip, the 2 lobes fused to the tip or nearly so (often notched at the tip), broadly triangular, the lower lip with the 3 lobes triangular, the lowermost lobe the longest. Corollas papilionaceous, glabrous, blue to purple, lilac, or pink (white in some cultivars), the banner usually with a white and/or yellow central portion, the wings and keel often darker, at least toward the tip, the banner with the expanded portion broadly obovate to nearly circular, with a pair of thickened areas or small hornlike appendages at the base, rounded to very broadly angled at the tip and often finely longitudinally keeled, abruptly arched upward toward the base or midpoint, the wings about as long as the banner, asymmetrically oblong to oblong-obovate, appearing curved, not fused to the keel, the keel about as long as the banner, obovate, boat-shaped, strongly curved upward, rounded to bluntly pointed at the tip. Stamens 10, all of similar lengths, 9 of the filaments fused and 1 filament free, the fused portion 10–12 mm long, curved upward abruptly near the tip, the free portion 3–5 mm long, the anthers small, attached at or near the base, all similar in size. Ovary 10–12 mm long, linear, short-stalked, encircled by a ringed nectar gland below the midpoint, glabrous or hairy, the style glabrous, the stigma terminal, small. Fruits legumes, narrowly oblong (few-seeded fruits sometimes appearing narrowly oblanceolate), flattened, stalked at the base, tapered to a beaked tip, the margins appearing somewhat wavy, irregularly indented between the seeds, the surfaces also indented between the seeds, glabrous or hairy, hardened or woody in texture, dehiscent (sometimes tardily so) by 2 valves, these becoming loosely spirally twisted, with (2–)4–12 seeds. Seeds circular to ellipsoid, somewhat kidney-shaped, or occasionally more or less oblong in outline, flattened, the surfaces reddish brown to black, smooth or with a few faint wrinkles, shiny. About 6 species, temperate North America, Asia.

Stritch (1984, 1985) segregated the Asian species into the genus Rehsonia Stritch. There are a number of minor morphological differences that might justify this action, summarized in the key below. However, the new genus was not supported with a full taxonomic treatment of the group and the name has not been widely adopted by other botanists . Those who have studied the group have uniformly concluded that the Asian and American taxa of Wisteria in the broad sense accepted here are each other’s closest relatives (Lavin and Sousa S., 1995; J.-m. Hu et al., 2002), but there has not yet been a detailed phylogenetic study of relationships among these taxa.

Several species of Wisteria are cultivated as ornamentals on trellises and arbors or trained as shrubs or trees. Care must be taken to provide a sturdy substrate for climbing plants, as the mass of stout stems can grow to be very heavy. The beautiful flowers are strongly scented and the volatile oils are used as a fragrance component in perfumes, soaps, incense, and other items. Strips of bark have been used in the manufacture of cloth, string, and handcrafts, especially basketry. The flowers are sometimes eaten, either fresh in salads or battered and fried (Stritch, 1985). However, in particular, the seeds apparently are moderately toxic, causing a variety of symptoms, including headache, dizziness, sweating, and severe distress of the digestive system (Burrows and Tyrl, 2001).