Common moonseed is a rather slender, twining vine with stems to 16 feet long or more, that climbs or sprawls. It occurs nearly statewide. It bears clusters of bluish-black fruits. The seeds are flattened, with a raised edge shaped like a crescent moon.
Leaves are alternate, simple, triangular or kidney-shaped, 2–6 inches long and wide, unlobed or with 5 or 7 shallow lobes; tips of lobes blunt or with an abrupt, minute sharp point; base heart-shaped to flattened; the point of the leaf stalk’s attachment is not on the margin but is on the lower surface of the leaf, near the margin; 7 or 9 main veins originate at the leaf stalk’s point of attachment; margin lacks teeth; upper surface dull green, smooth; lower surface much paler green, pale gray or silvery gray, smooth to thinly hairy; leaf blade firm and rather thick; leaf stalk slender, elongate, about as long as the blade.
Stems are slender, twining, reddish brown or greenish brown, shiny with fine grooves and ridges, slightly hairy to smooth later; tendrils absent.
Bark is reddish brown to greenish brown, smooth on young stems; brown to grayish brown, scaly or warty with short ridges of corky bark near the base of old stems; vine herbaceous above, somewhat woody near the base; wood soft, white.
Flowers May–June, in loose, drooping clusters along the leaf axils of new growth; both male and female flowers are present in separate clusters; flowers numerous, often 40–50, greenish white to white, smooth; petals 4–12, white, broadest above the middle; stamens 18–20, slightly extending beyond the flower, stamens not well developed in the female flowers.
Fruits September–October, in a grapelike cluster, about ¼ inch in diameter, dark blue to black with a whitish coating that can be rubbed off, globe-shaped, somewhat flattened on the sides; flesh thick, juicy, the skin tough; seeds solitary, yellowish, circular, crescent-shaped, flattened; fruit somewhat poisonous if eaten.
- Carolina moonseed is a close relative, but it has clusters of bright red (not bluish-black) berries, and the leaf stem attaches to the edge of the leaf blade (not on the lower surface of the leaf blade).
- Moonseed fruits may easily be confused with our various species of wild grapes (Vitis spp.). Because wild grapes are edible and moonseeds are toxic if eaten, it is important to be able to distinguish between these plants.
- Key characters for identifying grapes are their toothed leaves, the curling tendrils by which they climb, and their seeds, which are not disk-shaped or bowl-shaped.
- Unlike grapes, common moonseed has the leaf lobe tips with an abrupt, minute sharp point, but the leaf margins are not toothed.
- Bur cucumber (Sicyos angulatus) is another native vine with lobed leaves something like moonseed’s, but it is an herbaceous annual (not a woody vine), and its spiny, burlike fruits are quite different.
Habitat and Conservation
This native vine may be grown on a trellis or other support, as a ground cover sprawling on the ground, or on banks to control erosion. It is best used in naturalized settings. It is not recommended to plant this vine in a yard because the fruits, which resemble a cluster of grapes, are considered toxic to some people and should be kept from the reach of children and pets.
An extract of the fresh roots has been used as a laxative and as a treatment for syphilis, rheumatism, gout, and skin infections. The roots have been used as a substitute for sarsaparilla and are said to have tonic properties and to increase urine flow. All parts of the plant are toxic to humans if eaten.
The genus name, Menispermum, is a combination of the Greek words meni (“moon”) and spermum (“seed”), in reference to the moon-shaped seed; the species name, canadense, denotes its presence in Canada, where it may have first been found.
Common moonseed’s presence contributes to the richness of its bottomland forest habitat. Bottomland forests provide hunting, fishing, botanizing, and bird-watching opportunities, as well as pleasant, shady put-in and camping sites for boaters, rafters, and canoeists.
The fruit is seldom eaten by wildlife, though apparently several species of woodland birds may eat them, especially as the season progresses. Either more preferred foods run out, or perhaps the toxic alkaloids diminish over time. The birds pass the seeds undigested, so they distribute them away from the parent plant. The fruits are considered toxic to people and other mammals.
Apparently, flies and bees visit the flowers.
The moonseed moth (Plusiodonta compressipalpis) uses common moonseed as its larval host plant. The adults are tan, brown, and violet-gray moths with gorgeous swirly patterns. The caterpillars are gray, olive, and white inchworms that resemble bird droppings. The caterpillars chew through the leaf stems, then eat the leaves. Apparently, the caterpillars of this moth can only eat moonseed and its close relatives, so the females must find these plants and lay their eggs on them.
The larvae of at least one type of long-horned beetle, Hyperplatys aspersa, have been recorded feeding under the bark of moonseed, as well as other woody plants.
Common moonseed is one of many plants characteristic of Missouri’s bottomland forest and streamside habitats. These habitats, and the plant communities that grow in them, are crucial buffers for absorbing the scouring impact of high-energy floods. They protect levees, which protect cropland and other areas of interest to people. Where bottomland forests absorb low-energy floods, rich, deep sediments accumulate, creating highly prized, fertile cropland. Lowland vegetation also protects water quality by preventing soil from being washed into streams and by absorbing nutrients, fertilizers, and pollutants.
This vine is a component of thickets, and thickets are tremendously valuable to wildlife. Many small mammals, songbirds, and other animals find shelter and nesting space in these tangled jumbles of stems and leaves. Among the many kinds of plants that form thickets are those with seeds and fruits that feed these animals. A diverse array of insects feed on the plants, and their bodies become food for birds and their hungry nestlings.