WHAT IS AN ALLELOPATHY?
© 2005 Louis-M. Landry
University of Idaho Archive,
University of Idaho, Bugwood.org
a.k.a. C. maculosa
David Cappaert, Michigan State University,
Leslie J. Mehrhoff, University of Connecticut,
Swallow-worts may have harmful
effects on the native Monarch
Butterfly. They can compete with
and displace Common Milkweed, a
major food source. Swallow-worts
also attract and stimulate female
monarchs to deposit their eggs on
them even though the larva cannot
develop on these plants.
Pale and Black Swallow-worts
Less than common in their native ranges, swallow-worts are quite successful in New York state. Their seeds are easily dispersed by wind and by attaching to animal fur. Swallow-worts are typically most invasive in natural areas in the state. There they can compete with native plants for light and other resources. Once established, they spread rapidly and can completely cover native vegetation. Swallow-worts grow in a variety of situations and can be problematic in horticultural nurseries, perennial crops, pasture lands, and other disturbed areas. Chemicals they produce can negatively affect the survival of Monarch Butterfly (Danaus plexippus) larvae and resident soil microbial communities. The chemicals also may be toxic to wildlife and livestock that feed on swallow-worts.
Scientists are performing a variety of research on these allelopathic vines to learn how to control their spread. This research includes how to dispose of plants, especially their seeds. More long-term studies involve trying to understand the plants’ biology and ecology. This knowledge may help identify weaknesses in the plants’ structure or life cycle.
Swallow-worts are somewhat unique plants because some of their seeds have more than one embryo. This is called polyembryony. This feature results in the production of “sister seedlings” from a single seed. In the image, note the four “sister seedlings” emerging from one Pale Swallow-wort seed. This characteristic substantially increases the population densities of these plants.
Swallow-wort vines often form tangled dense thickets, hence the nickname “Dog-strangling Vine.”