Mature common tansy plants are easily recognized by the flat-topped clusters of small, button-like, yellow flowers they bear in the summer Common tansy is often confused with Tansy ragwort (Senecio Jacobea), a poisonous pasture weed and statewide noxious weed. Tansy ragwort can be distinguished from common tansy by its ray flowers (petals), absence of sharp toothed leaves and the long fringe of soft white hairs found on the seeds

Also known as golden buttons and garden tansy, is a perennial herb in the sunflower family. This species, native to Europe, has a long history of medicinal use. It was first introduced to North America for use in folk remedies and as an ornamental plant.

The plants contain alkaloids that are toxic to both humans and livestock if consumed in large quantities. Cases of livestock poisoning are rare, though, because tansy is unpalatable to grazing animals. Human consumption of common tansy has been practiced for centuries with few ill effects, yet the toxic properties of the plants are cumulative and long term consumption of large quantities has caused convulsions and even death. In addition, hand pulling of common tansy has been reported to cause illness, suggesting toxins may be absorbed through unprotected skin.

Common tansy is an invader of disturbed sites and is commonly found on roadsides, fence rows, pastures, stream banks and waste areas throughout North America. It may threaten the ecological health of these areas through reduction in livestock forage, wildlife habitat and species diversity. Common tansy is listed as
a noxious weed in Montana.

Biology: Common tansy spreads mainly by seeds, and less commonly from creeping rhizomes, to form dense clumps of stems. Each stem grows a cluster of numerous disc flowers during midsummer. These persist throughout the summer and into early fall. Pollination occurs through a variety of insects—flies, butterflies, moths and honeybees.
Grazing on lands infested with common tansy will not reduce its prevalence because common tansy is unpalatable to livestock. Improper grazing in these areas will reduce the density of desirable species and provide opportunities for the spread of common tansy.