This is yet another species which was imported from Europe for cultivation, but escaped to become an invasive and noxious weed. But, to give it what’s due, it is a handsome plant, providing texture and color in the disturbed ground habitats where it flourishes.
This is an upright, perennial plant, with rhizomes that form large colonies. The branching stems have ridges. The leaves, which have a strong, sharp odor of camphor, are alternate, and the leaflets are twice divided into deep lobes. The flowers are yellow, flat, rayless disks, which can number in the dozens.
Beyond some aphids, both introduced and native, and some introduced leaf miner flies and Pentatomidae (stink bugs) Tanacetum vulgare has no natural enemies in North America, though there are several insect species in its native territory which have evolved systems which can handle the toxic chemicals (primarily thujone) it contains.
In fact the insecticidal properties of Common Tansy are one of the reasons it was cultivated. It has often been planted alongside row crops, particularly potatoes, to discourage insect pests. In 19th century New England it was a common practice to pack coffins with it to protect the body from the invertebrates that were thought to decompose it. Its essential oils were mixed with alcohol and other herbs as a moderately effective mosquito repellent. And, throughout history, it was frequently placed in bedding to drive out lice and other scourges.
Despite its high toxicity (as little as a 1/2 oz of the essential oil can kill an adult human), Tanacetum vulgare has been used in herbal medicine dating back at least to the Greeks, primarily as a bowel cleanse to get rid of worms, and as an abortifacient.
Size- Up to 5’ tall
Habitat- Disturbed ground, agricultural ground, streambanks
Range- Region wide, except for the most arid parts of the interior
Blooms- Late summer into fall