Swallowworts - Cynanchum spp
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Flowers from June to July
Native originally to Europe (Italy, France, Portugal, and Spain)
The first collection of black swallow-wort in North America was from Ipswich, Essex County, Massachusetts, in 1854. An 1864 Essex County collector recorded that it was "escaping from the botanic garden where it is a weed and promising to become naturalized.” The fifth edition of Gray’s Manual of Botany reports black swallow-wort to be a weed escaping from gardens in the Cambridge Massachusetts area.
The flowers are self-pollinating. Fruits are soon produced, turning from green to light brown as they mature. The number of pods is directly related to the level of light available. When ripe, the fruits open along a seam and release flattened seeds equipped with downy parachutes that aid in wind dispersal. Black swallow-wort spreads long distances by seed and Local spread and establishment is through clones arising vegetatively from rhizomes. Thick infestations in full sun can produce 2,000 seeds per square meter. The seeds are polyembryonic with one to four embryos per seed which greatly increases the likelihood of seed survival and establishment. Wind dispersal of seed begins in late July to early August in open areas and continues throughout late summer and fall. Populations growing under dense wooded canopy may have inadequate resources to produce flowers or seeds. Black swallow-wort dies back to the ground every winter.
Website, video, and graphics by Rob Nelson
For more information on this plant or management please contact US Army Corp of Engineers