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American wisteria's flowers occur in showy terminal racemes. The flowers have 1/2" long pedicels that are densely covered with stiff hairs and some club-shaped, stalked glands. Individual flowers consist of a 1/4-3/8"white to pale green, hairy calyx and 15-20 mm long bluish-purple, pea-like, hairless flowers. The expanded portion of the banner (or standard) is bent backwards so it is perpendicular to the axis of the rest of the flower; the two lateral petals cover the keel like a hood. There are 10 stamens with tiny anthers, an ovary encircled by a nectar gland, and a single style hidden within the keel; nine of the 10 stamens are fused to each other, the tenth is free. The fruits are 2.75-4" long pea-like, hairless green pods containing 4-8 kidney-shaped or oval seeds, each about 8 mm wide; the pods are brown and the seeds are black when mature. The seeds contain an alpha-amino acid called canavanine which is structurally similar to L-arginine and the pods contain a saponin called wisterin; neither is a good thing to ingest. I've only seen American wisteria growing on the fence west of Japanese Garden. Periodically, the Park District cuts it down, I suspect because they fear for the fence's structural integrity (it's a heavy plant), but I wish a better solution could be found given American wisteria's rarity.

Wisteria

Wisteria frutescens

American wisteria [Blooms: May-Oct]