Pale swallowwort also may harm forest regeneration.
Research has shown that the reddish-flowered pale swallowwort grows rapidly in fields and forest edges but also invades understories, whereas the purple-flowered black swallowwort prefers habitats with more daylight.
The researchers wanted to determine whether both swallowwort species use a similar allelopathic strategy in displacing native plants.
Their previous work showed that the roots of pale swallowwort contain antofine, a compound believed to have some antifungal, antibacterial, and cytotoxic properties.
In further experiments, they exposed lettuce seedlings to a variety of swallowwort extracts and found that one of the extracts, which contained antofine, inhibited growth of lettuce roots.