Knotweed family (Polygonaceae)
Description: This vine is a summer annual up to 6' long. It branches frequently at the base and less often elsewhere. The slender stems are light green to reddish green and hairless. They have the capacity to twine about the stems of adjacent plants and the wire of fences. The alternate leaves are widely spaced along the stems and have long slender petioles. They are up to 2½" long and 1" across, cordate or sagittate, smooth along the margins, and hairless. Their texture is rather thin and delicate. At the base of each petiole is a membranous sheath (ocrea) that wraps around the stem. This sheath is rather short and hairless. Individual or pairs of flowers develop from the axils of the upper leaves on short slender petioles. Short terminal racemes of flowers about 1-2" long also develop from some of the upper stems. These flowers are about ¼" long and have 3-5 petal-like sepals that are greenish white, white, or light pink. Each sepal is slightly keeled along its outer surface. Each flower matures into a 3-angled achene that is oblong, but widest in the middle. It is only slightly winged or keeled. The flowers develop and mature rather quickly on young stems where new growth occurs. The blooming period occurs during the summer and lasts 2-3 months. Each fertile flower is replaced by a large black achene that is 3-sided; the surface of this achene is dull along the sides, but shiny along the angles. The root system consists of a slender branching taproot. This plant spreads by reseeding itself.
Cultivation: Full or partial sunlight, mesic conditions, and fertile loamy soil are preferred, although this plant can be found on poor soil as well. Germination of the seeds doesn't occur until late spring or early summer, but once it begins, the growth of the vines is rapid. Even small vines can produce viable seeds in a short period of time.
Range & Habitat: The non-native Black Bindweed is a common plant in central and northern Illinois, but less common or absent in some southern areas of the state (see Distribution Map). Habitats include cropland, fallow fields, fence rows, gardens and edges of yards, areas along railroads and roadsides, and miscellaneous waste areas. This plant is adventive from Eurasia. It is a common pest where the soil has been turned over for the cultivation of crops, vegetables, or annual flowers.
Faunal Associations: Little information about insect pollinators is available for Black Bindweed, although the flowers of a closely related species, Fallopia scandens (Climbing Buckwheat), are visited by short-tongued bees, wasps, and flies. The caterpillars of the butterfly Lycaena helloides (Gray Hairstreak) eat the achenes, while the foliage is eaten by the caterpillars of several species of moths. The seeds of Black Bindweed and the closely related Knotweeds are popular sources of food for several upland gamebirds and granivorous songbirds (see Bird Table). The seeds are also eaten by small rodents, including the Thirteen-Lined Ground Squirrel and White-Footed Mouse.
Photographic Location: Along a wire fence of the wildflower garden at the webmaster's apartment complex in Urbana, Illinois.
Comments: The foliage and vine-like growth of Black Bindweed has a striking resemblance to the Convolvulus spp. (Bindweeds) and Ipomoea spp. (Morning Glories). However, Black Bindweed is a shorter and less robust vine and its flowers have a dramatically different appearance from the flowers of the preceding species. The Fallopia spp. (Climbing Buckwheats) are vines with a climbing habit, unlike the closely related Persicaria spp. (Smartweeds) and Polygonum spp. (Knotweeds). Unlike Black Bindweed, the other Fallopia spp. that occur in Illinois are robust perennial vines that can become 20' long. Like many Rumex spp. (Docks), their achenes have conspicuous membranous wings, while the keeled achenes of Black Bindweed are without wings. Another scientific name for Black Bindweed is Polygonum convolvulus.