American Hog Peanut, Hog Peanut, Southern Hog Peanut, Wild Peanut

Amphicarpaea bracteata

am-fee-KAR-pay-uh  brak-tee-AY-tuh

Synonyms of Amphicarpaea bracteata (37) (Updated on 12-17-23 from Plants of the World Online): Amphicarpaea bracteata var. comosa (L.) Fernald (1937), Amphicarpaea bracteata var. pitcheri (Torr. & A.Gray) Fernald (1936),  Amphicarpaea bracteata var. typica B.Boivin & Raymond (1943)(not validly publ.), Amphicarpaea chamaecaulis B.Boivin & Raymond (1942), Amphicarpaea ciliata Raf. (1836), Amphicarpaea comosa (L.) G.Don, J.C.Loudon (1830), Amphicarpaea cuspidata Raf. (1836), Amphicarpaea deltifolia Raf. (1836), Amphicarpaea elliotii Raf. (1836), Amphicarpaea heterophylla Raf. (1836), Amphicarpaea monoica (L.) Elliott ex Nutt. (1818), Amphicarpaea monoica var. comosa (L.) Eaton (1822), Amphicarpaea pitcheri Torr. & A.Gray (1838), Amphicarpaea sarmentosa Elliott ex Nutt. (1818), Amphicarpaea villosa Raf. (1836), Cryptolobus americanus Spreng. (1826), Cryptolobus sarmentosus Spreng. (1826), Falcata bracteata (L.) Farw. (1924), Falcata caroliniana J.F.Gmel. (1792), Falcata comosa (L.) Kuntze (1891), Falcata pitcheri (Torr. & A.Gray) Kuntze (1891), Glycine bracteata L. (1753), Glycine comosa L. (1753), Glycine elliptica Sm. (1797), Glycine filosa Hornem. (1815), Glycine heterocarpa Hegetschw. (1813), Glycine monoica L. (1763), Glycine sarmentosa Roth (1800), Lobomon acutifolium Raf. (1836), Lobomon montanum Raf. (1836), Lobomon obtusifolium Raf. (1836), Lobomon sarmentosum Raf. (1836), Phaseolus monoicus Eaton & Wright (1840), Phaseolus pitcheri (Torr. & A.Gray) Eaton & Wright (1840), Savia volubilis Raf., Med. Repos. (1808), Tetrodea comosa Raf. (1836), Tetrodea monoica Raf. (1836)

Amphicarpaea bracteata (L.) Fernald is the accepted scientific name for the American Hog Peanut. It was named and described as such by Merritt Lyndon Fernald in Rhodora; Journal of the New England Botanical Club in 1933. It was first described as Glycine bracteata by Carl von Linnaeus in the second volume of the first edition of Species Plantarum in 1753.

The genus, Amphicarpaea Elliott ex Nutt., was described by Thomas Nuttall in The Genera of North American Plants in 1818. He gave credit to Stephen Elliott for previously naming the genus.

As of 12-17-23 when this page was last updated, Plants of the World Online lists three species in the genus Amphicarpaea. It is a member of the plant family Fabaceae with 793 genera. Those numbers could change as updates are made on POWO.

The above distribution map for Amphicarpaea bracteata is from Plants of the World Online. Areas in green show where the species is native. The map on the USDA Plants Database is similar and also includes the state of Montana (with no data) and Wyoming from a sighting in one county.

The map on iNaturalist shows where members have made observations. Anyone can join and it is a great website to confirm and share your observations. The maps on iNaturalist are continually updated as members post new observations.

THERE ARE SEVERAL LINKS AT THE BOTTOM OF THE PAGE FOR FURTHER READING AND TO HELP WITH A POSITIVE ID.

Hello, everyone! On September 2 (2022), I was walking along the fence on the south side of the farm looking at the Hops vine when I noticed something weird I had not seen before. The fence is covered with Japanese Honeysuckle but these strange-looking flowers were also in the mix. Well, it was quite obvious they weren’t from the honeysuckle, so I started looking for other leaves. I finally found a few plus some seed pods. The leaves were trifoliate like a bean.

I had not encountered this species before, so I uploaded the photos on iNaturalist. It turned out to be Amphicarpaea bracteata, commonly known as the American Hog Peanut or simply Hog Peanut. I didn’t read much about them until I initially wrote this page, so I was somewhat confused as to why it was called a Hog Peanut.

Apparently, this species produces two types of flowers and the genus name is Greek for “two-seeded” referring to two types of seeds… Above and below ground. Hold on a minute! Above and below ground?!?!?! It not only produces two types of seed but also two types of flowers. Flowers that grow on the vine, and flowers that grow from stems that creep along the ground. While the upper flowers are normal (chasmogamous), the lower flowers are cleistogamous, which means fertilization occurs inside a permanently closed flower. These flowers are inconspicuous and have no petals…

Chasmogamous flowers are produced in racemes of up to 15 flowers from the leaf axils (nodes). When you first see the flowers, you’ll likely be scratching your head for an explanation. I have seen a lot of weird flowers and these have to in the top five of WEIRD. Most sites describe two types of flowers, while Tropicos Flora of Missouri says 2 or 3. I’m just going to stick with two… 

Corolla with 5 petals, a 4-lobed calyx with 5 sepals (3 united more than half their length, upper two united full length), several stamens, and a pistil. They have a pea-like structure with an upright banner (often folded backward), two lateral wings, and a keel that is turned upward. The corollas can be purplish, light lavender, to white. 

On lower parts of the plant, “cleistogamous” flowers are often produced, sometimes even below the soil surface. These do not open and are self-pollinated. 

Amphicarpaea bracteata is an interesting native North American annual. It can be found in open woodlands, thickets, along fence rows, and so on. Some information indicates it is a tropical American wildflower, but according to the maps, that is somewhat misleading. It has quite a range for it to be a tropical species. 

Two varieties were recognized, Amphicarpaea bracteata var. bracteata and Amphicarpaea bracteata var. comosa with subtle differences. The latter, var. comosa, is now considered a synonym, and var. bracteata was the autonym (an automatically generated name when an infraspecific taxon is named). Many botanists don’t accept the division due to free intergradation, absence of geographical correlation, and frequent mixed populations.

Amphicarpaea bracteata prefers full sun to light shade in open woodlands, along fencerows, thickets, along streams, ditches, sandy meadows, and so on. They prefer ample moisture but are somewhat drought-tolerant to a certain degree. I know that because of where and when I found them on the farm.

The fruit (seed pods) of the upper flowers contain 2-3 seeds, while those of the lower flowers only have one. What is even weirder, is that they burrow into the ground. Information I read on one site (Climbers by the University of Michigan) that E.J. Trapp’s description in the American Journal of Botany (1988) says “runners (ground level stems) are produced that search out dark crevices in the soil. If these are found, the plant produces an underground flower.” How weird is that?

I went back to the fence on October 1 to get a few more photos… I knew I had to find a vine with three leaves that wasn’t Poison Ivy…

I found it in a spot I hadn’t noticed before climbing up ragweed. Three leaves like a bean, kind of heart-shaped, with smooth margins. Not like Poison Ivy…

Twining vines spiral around other plants like beans, they do not have tendrils like peas.

This is a twining species that grows vines from 2-5’ long. The stems can be either light green to reddish green, hairless (glabrous) to densely hairy (pubescent) with antrorse (turned inward) to spreading hairs. White appressed hairs were characteristic of var. bracteata, while var. comosa were said to have light brown spreading hairs. 

I looked through the stems growing along the ground to see if I could find the mysterious, inconspicuous flowers with no petals, but couldn’t find any. I wonder if I get a shovel if I could find the seeds that bury themselves? Hmmm…

Amphicarpaea bracteata, as with other members of the plant family Fabaceae, have alternate pinnately trifoliate leaves. In other words, the leaf has three leaflets attached to the main stem by a long petiole (leaf stem) that grows alternate to one another along the stem. The leaves are said to be ovate to ovate-rhombic in shape, as they are broader below the middle, and taper to a pointed to bluntly pointed tip. The terminal leaves grow up to 2 1/2-4” (var. comosa somewhat bigger), while the lateral leaflets are smaller. The leaflets can also be variable in shape are are attached to the petiole by 1/8” (or so) petiolules. The leaves can be hairless (glabrous) to pubescent (hairy) with short appressed hairs, giving them a rough texture. At the base of each petiole are a pair of stipules… 

I did manage to find four seed pods in a cluster…

Fertile chasmogamous flowers produce flattened seed pods that are up to 1 1/2” long and contain 2-4 oblong seeds. The cleistogamous flowers produce very large, fleshy, and 1-seeded fruit.

Yep, the seeds are small.

I suppose I should get a shovel to see if I can find underground seeds…

The summer of 2023 was very hot and dry. I didn’t see any of this species and most wildflowers had fizzled out from the heat and drought by mid-summer.

Hopefully, I will find this species again in 2024 so I can take more and better photos

I live on the family farm in Windsor, Missouri where I enjoy gardening, collecting plants, and identifying wildflowers. The farm is in Pettis County but Henry County is across the street, and Benton and Johnson aren’t far away. I have grown over 500 different plants and identified over 250 species of wildflowers (most have pages listed on the right side of the page). I am not an expert, botanist, or horticulturalist. I just like growing, photographing, and writing about my experience. I rely on several websites for ID and a few horticulturalists I contact if I cannot figure them out. Wildflowers can be variable from location to location, so that can be a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.

I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at thebelmontrooster@yahoo.com. I would enjoy hearing from you especially if you notice something is a bit whacky.

FOR FURTHER READING:
PLANTS OF THE WORLD ONLINE (GENUS/SPECIES)
INTERNATIONAL PLANT NAMES INDEX (GENUS/SPECIES)
TROPICOS (GENUS/SPECIES)
FLORA OF MISSOURI (SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
USDA PLANTS DATABASE
USDA PLANT GUIDE
DAVE’S GARDEN
MISSOURI PLANTS
iNATURALIST
WILDFLOWER SEARCH
ILLINOIS WILDFLOWERS
MINNESOTA WILDFLOWERS
KANSAS WILDFLOWERS AND GRASSES
PFAF (PLANTS FOR A FUTURE)
GO BOTANY
LADY BIRD JOHNSON WILDFLOWER CENTER
FRIENDS OF THE WILDFLOWER GARDEN
UNIVERSITY OF WISCONSIN
MARYLAND BIODIVERSITY PROJECT
CLIMBERS-UNIVERSITY OF MICHIGAN

NOTE: The data (figures, maps, accepted names, etc.) may not match on these websites. It depends on when and how they make updates and when their sources make updates. Some websites have hundreds and even many thousands of species to keep up with. Accepted scientific names change periodically and can be hard to keep with as well. Some of the links may use a name that is a synonym on other sites. In my opinion, Plants of the World Online by Kew is one of the most reliable and up-to-date plant databases and they make updates regularly. I make updates “at least” once a year and when I write new pages or add new photos but I do get behind. We are all a work in progress. 🙂