Not All Non-native Plants are Invasive Plants
Invasive plant species are a problem because they interfere with native landscapes as well as the intentional landscapes in our gardens and parks. As the USDA puts it, “…not all exotic species are considered harmful. Non-native plants are fundamental to our lifestyle – most of our food crops, such as potatoes and wheat, are not native to the United States. Invasive species, however, are exotic organisms that have gone beyond being useful and have become harmful…There are some benefits to all species – but invasive species do more harm than good.”
Many invasive plants, such as Japanese barberry or Norway maples are actually illegal to sell in Massachusetts, and the City does not plant invasive species in its parks and open spaces. You can find a list of Massachusetts invasive species here: https://www.mass.gov/service-details/invasive-plants
Black Swallow-Wort, A Threat to Monarch Butterflies
One of the most aggressive and harmful invasive plants is the Black Swallow-wort (BSW), Cynanchum louiseae, sometimes referred to as Cynanchum nigrum or Vincetoxicum nigrum). Though native to Southwestern and Northern Europe, BSW is easy to find in Somerville. A member of the same plant family as the milkweeds native to New England, BSW grows rapidly and aggressively, covering other vegetation and taking over urban fences as well as rural woodlands. BSW is aggressive and harmful in a variety of ways: it releases biochemicals into the soil that prevent the establishment of other plant species. Its seeds are carried on the wind or transported by water; its roots are toxic to some mammals; and, its plants toxic to many insect larvae.
One insect that suffers from BSW’s toxicity are monarch butterflies. These beautiful and well-known pollinators migrate in North America, from Mexico to the US. Already challenged by a loss of winter habitat and host plants, as well as the erratic climate changes in the last decade, BSW provides another threat to their survival. Although monarchs feed on the nectar of many flowers, they lay their eggs only on certain types of milkweed plants (a number of species of Asclepias are native to Massachusetts). Because of the similarity of BSW to milkweed though, female monarchs sometimes lay their eggs on BSW, but BSW leaves are toxic to the caterpillars that hatch from the monarch eggs so they die.
Fortunately, awareness has grown about BSW in recent years and a number of folks have committed to pulling and properly disposing of the noxious weed. Both the Somerville Garden Club and the Cambridge Pod Patrol have been working to eradicate BSW. You can help them by getting involved in their events, pulling BSW in your yard and, if you want to help the monarchs, replacing them with the native milkweeds. Visit their sites linked to above for images and more information on how you can help with this effort.
