Family: Fabaceae (the bean and pea family)
Common Names: hog peanut, American hog-peanut, wild peanut
Etymology: Amphicarpaea is Greek for “two-seeded,” referring to the two types of seeds: above and below ground. Bracteata is Latin for “bearing bracts” (1, 3).
Glycine bracteata Linnaeus (2)
Amphicarpaea monoica (L.) Ell.
Falcata comosa (L.) Kuntze (4).
Quick Notable Features:
- Trifoliate vine without tendrils
- Narrow, pointed, pale purple or white papilionaceous flowers
- Flowers produced also at ground level to produce underground “peanut”
Plant Height: up to 150cm in length (1)
Subspecies/varieties recognized (12):
A. bracteata (L.) Fernald var. comosa Fernald
A. bracteata (L.) Fernald var. pitcheri Fassett
A. bracteata (L.) Fernald var. typica B. Boivin & Raymond
Most Likely Confused with: Other trifoliate legumes such as Apios americana, Desmodium rotundifolium, Lespedeza procumbens, Pueraria lobata, and Strophostyles helvola, as well as other trifoliate non-legumes such as Toxicodendron radicans.
Habitat Preference: reported from dry to moderate and even moist areas such as woods, forests, meadows, roadsides, and prairies (1, 5).
Geographic Distribution in Michigan: The hog peanut has been documented throughout the southern portion of the lower peninsula of Michigan but is not reported from many of the northern counties. It is, however, reported from at least five counties in the Upper Peninsula and may be frequently overlooked (5).
Known Elevational Distribution: The species was found in Haywood, NC at 760 meters above sea level (14).
Complete Geographic Distribution: Native to Canada and the United States: Manitoba east to Nova Scotia, south to Florida, west to Texas, and north to North Dakota and Montana (3).
Vegetative Plant Description: A. bracteata is an annual or perennial plant that grows from a taproot (3,5,13). The coiling stem fixes the plant to its support without the use of modified tendrils. The plant can be either glabrous or can bear appressed pubescence. The grooved stipules are approximately 0.4cm long, and oblong to ovate (15). The alternate leaves that bear a long petiole (2-10cm) are trifoliate. Each of the three leaflets are broadly oval (slightly longer than broad), acute, with the lateral leaflets inequilateral and terminal leaflet bearing a longer petiolule than the other two (5,15). The leaflets bear stipelets and the leaflet size is 2-6cm long (13).
Climbing Mechanism: A. bracteata twines using the apical portion of the stem, twining in a dextral orientation (left to right) (pers. obs. R.J. Burnham, see image).
Flower Description: The four fused sepals, glabrous or appressed pubescent, are slightly asymmetric and appear to number four through fusion forming a calyx tube 4-5mm long. The five petals are white to lavender, zygomorphic, 12-18mm long. Each flower has a short pedicel and is subtended by small, ovate bracts (2-2.5mm long) that equal or are slightly shorter than the pedicels. The wings are wider at the tip than the base. The upper inflorescences (in which this flower type is borne) form a loose unbranched, nodding raceme in the leaf axils bearing 2-15 flowers. Stamens are 10 in two groups: one of 9 fused by their filaments and the second group of one. The simple, single pistil has a superior ovary and filiform style 1-3mm long (1, 3, 5, 8, 9,13,15).
There is, however, a second type of flower produced. They are borne solitary on the lower or creeping branches, near the soil level and are relatively inconspicuous flowers that lack petals (3). Flowers produced near the ground produce a pod that buries itself just below soil level (4).
Flowering Time: Aug.-Sept in our area (1,3).
Pollinator: The lower flowers do not open and are believed to be cleistogamous (5, 7). It is reported that selfing flowers are sometimes borne from the upper inflorescences as well (6,7).
Fruit Type and Description: The 3-seeded aerial fruits are 1.5-4cm long, flat, smooth to strigose, wider at the tip, and pointed at both ends (persistent style) (1,9). Fruits produced at or below the ground level are only 6-12mm, strigose, and contain a single seed (3,4,9,13).
Seed Description: The underground single-seeded pods produce hard seeds up to 15mm in diameter. Birds feed on the seeds of both kinds of fruit. Hogs eat the seeds of the fruit below ground, thus the common name (3). Seedlings bear simple leaves as the first leaves to show above ground but are rapidly replaced by typical trifoliate leaves (see image).
Dispersal Syndrome: Trapp (6) found that the seeds of both types of fruits are ballistically dispersed, with the aerial fruits dispersing seeds furthest because of the height advantage. He also reports that both chasmogamous and cleistogamous flowers are produced above ground. He described the subterranean fruits as being single seeded and 16 times heavier than those produced above ground.
Distinguished by: A. bracteata is clearly distinguished from Pueraria lobata by the leaflet size: Amphicarpaea bracteata leaflets are about 1.5 to 4 cm long, whereas P. lobata leaflets are 10-20cm. Strophostyles helvola bears a minute point at the tip of the leaflets and has umbellate inflorescences. Desmodium rotundifolium fruits easily break between seeds whereas those of A. bracteata do not segment. In addition, the leaflets of Desmodium are much more rounded than seen in the hog peanut. Apios americana is clearly 5-7 foliate, not trifoliate. Toxicodendron radicans has irregularly rounded lobes or large broad teeth on the leaflets, which are generally much larger than those of A. bracteata.
Other members of the family in Michigan (number species): Wisteria (1), Amorpha (2), Amphicarpaea (1), Anthyllis (1), Apios (1), Astragalus (3), Baptisia (4), Caragana (1), Cercis (1), Chamaecrista (2), Cladrastis (1), Colutea (1), Crotalaria (1), Cytisus (1), Dalea (1), Desmodium (12), Genista (1), Gleditsia (1), Glycine (1), Gymnocladus (1), Hedysarum (1), Kummerowia (1), Lathyrus (10), Lespedeza (13), Lotus (1), Lupinus (2), Melilotus (2), Mimosa (1), Orbexilum (1), Phaseolus (2), Pisum (1), Pueraria (1), Robinia (3), Securigera (1), Senna (1), Strophostyles (1), Tephrosia (1), Trifolium (9), Vicia (7), Vigna (1) .
Ethnobotanical Uses: The seeds can be used as a peanut substitute. Some authors report the seeds of the upper fruit are inedible, but that those from the underground fruit as edible when boiled (3). Other reports indicate that the underground seeds can be harvested throughout the winter and can be eaten raw or cooked (4), whereas flowers higher up on the plant produce seeds that are much smaller and are usually cooked before being eaten. The seeds can be used in all the same ways as lentils and are a good source of protein (4).
The hog peanut was used by native Americans such as the Pawnee, Chippewa, and Cherokee for a variety of uses such as tea for snakebite (root) and diarrhea (root infusion), swellings (poultice of leaves) as well as a food source (4, 5).
Phylogenetic Information: Amphicarpaea bracteata is a member of the Fabaceae, subfamily Faboideae. Families Fabaceae. Polygalaceae, Quillajaceae, and Surianaceae form the Fabales order. The Fabales, Rosales, Cucurbitales, and Fagales form a monophyletic group within the Eurosids I within the larger Rosid group. All are eudicots are angiosperms (11).
Interesting Factoid: Trapp’s (6) description of the subterranean fruits indicated that they were single seeded and are 16 times heavier than those produced above ground. Runners (ground level stems) are produced that search out dark crevices in the soil. If these are found, the plant produces an underground flower (6).
Literature and websites used:
- Freckman Herbarium http://wisplants.uwsp.edu/scripts/detail.asp?SpCode=AMPBRA
- ITIS: Integrated Taxonomic Information System http://www.itis.gov/index.html Retrieved [31 July 2008], from the Integrated Taxonomic Information System on-line database.
- Native Plant Information Network, Lady Bird Johnson Wildflower Center website, http://www.wildflower.org/explore/ Information retrieved 31 July 2008.
- Plants For A Future, 1996-2008. Retrieved July 31, 2008 http://www.ibiblio.org/pfaf/cgi-bin/arr_html?Amphicarpaea+bracteata
- USDA, NRCS. 2008. The PLANTS Database, Version 3.1, National Plant Data Center, Baton Rouge, LA 70874-4490 USA. http://plants.usda.gov/ Accessed July 31, 2008
- Trapp, E.J. 1988. Dispersal of heteromorphic seeds of Amphicarpaea bracteata (Fabaceae). American Journal of Botany 75(10):1535-1539.
- Parker, M.A. 2002. Evolution in natural and experimental populations of Amphicarpaea bracteata. Journal of Evolutionary Biology 7(5):567-579.
- Gleason, H.A. and A. Cronquist. 1991. Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. Bronx, New York, USA: New York Botanical Garden Press.
- McGregor R.L. 1986. Flora of the Great Plains. Lawrence, Kansas, USA: The University Press of Kansas.
- Voss, E. G. 1985. Michigan Flora Part II: Dicots. Ann Arbor, Michigan, USA: Cranbrook Institute of Science.
- ANGIOSPERM PHYLOGENY GROUP 2003. An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141(4):399-436.
- The International Plant Names Index, 2004-2008. http://www.ipni.org.
- Fernald, M.L. 1950. Gray’s Manual of Botany, 8th ed. New York: American Book Company.
- Tropicos.org. Missouri Botanical Garden. 02 Nov 2012 <http://www.tropicos.org/Name/13015648>
- Britton, N.L. & H.A. Brown 1970. An Illustrated Flora of the Northern United States and Canada: Volume II. New York, NY: Dover Publications, Inc.
Image Credits (all used with permission):
- Image of the leaves and flowers, as well as the flower close-ups are courtesy of Merel R. Black, University of Wisconsin-Madison.
- Image of stem twining is courtesy of George H. Bruso, Lady Bird Johnson Wildflower Center. http://www.wildflower.org/gallery/result.php?id_image=8972
- Image of leaves only courtesy of Louis-M. Landry
- Image of seeds courtesy of Steve Hurst, USDA-NRCS PLANTS Database. ARS Systematic Botany and Mycology Laboratory, DC, Washington.
- Image of seedling © Robyn J. Burnham, University of Michigan, Ann Arbor, MI.
- Species distribution map, derived from the Michigan Flora Online.
PRIMARY AUTHORS: Robyn J. Burnham, ReBecca Sonday, John Bradtke, and Cristine Santanna. © Robyn J. Burnham, University of Michigan.