Black Bindweed is an introduced twining annual vine that can grow to 40 inches long. It is potentially invasive and is found sprawling on and on top of other plants for support. The stems branch at the base but less frequently above. The stem is light green to reddish-green, hairless, slightly angular, and the nodes lack bristles. The vine twines in a clockwise rotation, unlike the true bindweeds which twine counterclockwise.
The leaves are alternate on the vine, well spaced and have heart-shaped bases; the blade can be arrow-shaped to elliptic and they have long slender stalks that terminate in a sheath (an ocrea) that is cylindric and can be tan to greenish-brown and is smooth, without hair or bristles at the base.
The inflorescence is a short terminal spike-like cluster of stalked flowers, 3/4 to 2-1/2 inches long that occurs at the upper end of the stems. The flowers on the spike are separated into fascicles.
The flowers are very small, bisexual, 5-parted, 1/8 to 1/4 inch long including a small stipe-like base, in groups of 3 to 6 at each fascicle of the inflorescence; they have a greenish-white perianth whose base is sometimes pinkish to purplish. The flower lacks petals and the sepals have the color (called tepals). Each of the 3 outer tepals has a slight keel so that when the flower is closed it looks 3-angled. The inner two tepals are slightly smaller. There are 8 stamens, the filaments flattened at the base and several styles that join at the tips forming a head.
Seed: Mature flowers form a dry black 3-sided achene that lacks wings and resembles a kernel of buckwheat - which is how a number of alternate common names using 'buckwheat' came about. The seed surface is minutely granular and dull except on the angles which are shiny. Seeds are vital for a number of years. The flower is pollinated by insects that reach for nectar secreted by the glands at the base of the stamens.
Habitat: Black Bindweed grows in disturbed sites, roadsides and the fringes of cut areas with mesic conditions and full to partial sun. It is not rhizomatous but has a slender fibrous taproot. It can be aggressive in crop fields. While invasive, it is not however, as yet, listed as a restricted weed or noxious weed in Minnesota. (2018)
Names: The genus Fallopia is an honorary named for the early Italian anatomist, Gabriele Fallopi (1523-1562). He was professor of anatomy at Pisa and Padua. The species convolvulus, is from the Latin word convolvo, meaning 'to twine around'. A former synonym for this species was Polygonum convolvulus. Black Bindweed was separated from the genus Polygonum and placed in Fallopia which describes erect or climbing or sprawling fibrous rooted annuals and perennials which have ocreas that are never 2-lobed at the tip and the outer tepals that are winged or keeled. Molecular data show the two genus are close and thus, some authorities have not accepted the change. Minnesota authorities have done so, following the lead of Flora of North America.
The author names for the plant classification are as follows: The original classifier ('L') refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. He published in 1753 in the name Polygonum convolvulus. . His work was amended in 1970 by 'A.Löve' which refers to Áskell Löve (1916-1994) Icelandic botanist, co-founder of the Flora-Europaea project and professor at various universities in North America.
Comparisons: This is a short vine unlike others in the Fallopia genus found in Minnesota; the achenes do not have wings and the ocreas are without hair or bristles unlike Fringed Black Bindweed, Fallopia cilinodis, where the ocrea is bristly and the seed is shiny all over. It is quite similar to Climbing False Buckwheat, F. scandons, but there the fruiting perianth has wings and the seeds are shiny all over. The only other species in Minnesota is Japanese Knotweed, Fallopia japonica, an invasive introduced plant where the stems are erect and large. The clockwise twining also separates the Fallopia plants from the bindweeds in the Convolvulus genus where they twine counter-clockwise.
Above: 1st photo - The vine twines clockwise around available grasses and upright plants. Vines can have a reddish tinge of color. 2nd photo - The flower clusters are grouped at each fascicle of the inflorescence. The 3 outer greenish-white tepals have a keel giving the unopened flowers a triangular shape. These show a little pink near the base of each which is typical. The cluster in the 3rd photo is a more pinkish type.
Below: 1st photo - The vine twines always in a clockwise manner. Vines can have a reddish tinge of color. 2nd photo - The leaf nodes and stem nodes have a sheath (the ocrea) without hair or bristles. 3rd photo - leaves can be arrow-shaped to elliptic. The flower cluster in the lower section of the photo is Crown Vetch.
Below: 1st photo - The inflorescence is that the end of a stem. 2nd photo - Leaves have heart-shaped bases.
Below: The green perianth and the black seeds - the surface is dull and minutely granular, except that the angles are shiny
Notes: Black Bindweed is an import from Eurasia that has naturalized across all of North America except Nunavut. Within Minnesota there are very few counties where it has not been reported. There are eight species of Fallopia found in North America, twelve world-wide.
As a weed of cereal crops the plant is a pest as the angled seeds are injurious to forage animals digestive tracts if the seeds become mixed with normal cereal seeds which happens when the plant grows in grain fields.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"