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Cynanchum spp.
swallowwort
Overview
Cynanchum is a large genus of twining and climbing perennial herbs, vines, and subshrubs in the dogbane family (Apocynaceae), with somewhere between two and three hundred species spread through tropical and temperate regions worldwide. Most species twine anticlockwise to 3-10 feet (1-3 m), climbing over other vegetation, and exude a milky latex when cut. The opposite leaves are usually heart-shaped to lance-shaped, 1-5 inches (2.5-13 cm) long. Small five-lobed star-shaped flowers 0.1-0.4 inch (3-10 mm) across are borne in stalked clusters from the leaf axils and range from white and greenish to pink, maroon, and near-black depending on species. These are followed by slender paired follicles that split to release flat seeds, each carried on a tuft of silky hairs for wind dispersal. Several species, including the black swallowwort C. louiseae and pale swallowwort C. rossicum, have become aggressive weeds outside their native range, smothering vegetation and spreading by both seed and root. The milky sap of many species contains toxic compounds that deter grazing and can poison livestock. Because of this weedy and toxic reputation the genus is seldom cultivated, though a few species are grown in specialist collections.
Native Range
Cynanchum occurs naturally across the warmer parts of every inhabited continent, with major centres of diversity in Africa, Asia, and the Americas. Individual species are native to habitats ranging from tropical forest margins to temperate grassland and rocky slopes. Several Old World species have naturalised as invasive vines in North America.Suggested Uses
Most Cynanchum species are not planted deliberately and are managed as weeds, particularly the invasive swallowworts of North America. A few non-aggressive species are grown in specialist and botanical collections for their dark, star-shaped flowers. The flowers attract a range of small pollinating insects during summer.How to Identify
Appearance
Size & Dimensions
Height3' - 10'
Width/Spread3' - 6'
Bloom Information
Cynanchum flowers chiefly from late spring through summer, with many temperate species blooming June to August. The small starry flowers open in successive clusters over several weeks. Paired seed pods develop through late summer and split in autumn to release plumed seeds.
Detailed Descriptions
Flower Description
white, pink, to dark maroonFoliage Description
greenGrowing Conditions
Sun Requirements
Requires 4-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight