Amphicarpaea, commonly known as hogpeanut, is a small genus of twining herbaceous legumes in the family Fabaceae (subfamily Faboideae, subtribe Glycininae), comprising three species distributed across eastern North America and Asia. Its closest relatives within subtribe Glycininae are Glycine (the soybean genus) and Teramnus.
Plants are annual or perennial climbing herbs with pinnately compound leaves bearing three stipellate leaflets. They produce small, purplish to white flowers arranged in axillary racemes or panicles; each pedicel is subtended by a striate bract. The flower is typical of the bean subfamily, with an obovate standard, auricled wings, a nearly straight keel, and 10 diadelphous stamens. The primary fruits are flat, oblong, pointed pods usually containing three seeds.
The genus is particularly notable for its geocarpic reproduction: in addition to the aerial chasmogamous flowers, plants produce long, filiform, near-basal branches bearing small, nearly apetalous cleistogamous flowers that develop into small, often subterranean, one-seeded pods — a strategy that ensures seed set even when pollinators are absent.
Three species are recognised: Amphicarpaea bracteata (L.) Fernald, native to eastern North America; Amphicarpaea edgeworthii Benth., ranging across eastern and southeastern Asia (China, India, Japan, Korea, Russia, and Vietnam); and Amphicarpaea ferruginea Benth., found from Nepal through the eastern Himalayas, Myanmar, south-central China (Sichuan and Yunnan), and Thailand.
Etymology
The genus name Amphicarpaea derives from the Greek amphi (both, on both sides) and karpos (fruit), referring to the plant's distinctive production of two types of fruit: aerial pods from chasmogamous flowers and subterranean pods from cleistogamous basal flowers. An older synonym, Falcata, alludes to the curved form of its pods.
Distribution
Amphicarpaea has a disjunct distribution spanning eastern North America and Asia. A. bracteata occupies eastern North America; A. edgeworthii ranges across eastern and southeastern Asia including China, India, Japan, Korea, Russia, and Vietnam; and A. ferruginea is found from Nepal and the eastern Himalayas through Myanmar, south-central China, and Thailand.
Ecology
Plants grow as twining herbs in woodland edges, thickets, and moist to mesic forest understories. The genus employs a dual reproductive strategy: showy aerial flowers attract pollinators for cross-pollination, while inconspicuous basal cleistogamous flowers self-fertilise and develop small, often underground pods, providing reliable seed set regardless of pollinator availability.
Taxonomy Notes
Amphicarpaea is placed in subtribe Glycininae within subfamily Faboideae of Fabaceae. Phylogenetic analyses position its closest relatives as Glycine (soybeans) and Teramnus. The older genus name Falcata is a synonym. GBIF recognises three accepted species in the genus.
