Cynanchum louiseae

black swallowwort - These herbaceous, twining vines in the Dogbane family (Apocynaceae) form dense colonies that are almost impossible to eradicate, breaking apart when dug up. Black swallowwort has dark purple flowers with triangular petals, while pale or red swallowwort has pale-purple to yellowish flowers and petals almost twice as long as they are wide. Cutting off the flowers only delays the maturing of fruits, which cast seeds to the wind from seedpods that are similar to the pods of milkweeds, which are their close relatives. Swallowworts easily overwhelm open sites in wildlife sanctuaries, and along roadsides and railroads with comprehensive cover through which nothing else can grow. [image: (c) New England Wild Flower Society/ John Lynch]

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