Up at Paradise Meadows today I had the (unfortunate?) opportunity to photograph some common tansy (Tanacetum vulgare) growing along the roadside. Common tansy is an invasive perennial that grows in disturbed places, road edges and stream banks. WeedsBC reports that the common tansy is problematic especially in areas like interior BC so it was disconcerting to find it in the sub-alpine. The plant spreads by both seed and root material which is often transported by birds, animals and humans. According to the Invasive Plant Council of BC, seeds can remain viable for up to 25 years!
Common tansy is fairly easy to identify with distinctive “button like” flowers and fern-like leaves. Its flowers are comprised of disc flowers but lack ray flowers. In addition, it lacks basal leaves. These identification features are helpful to separate it from the native dune tansy (T. bipinnatum ssp. huronense) discussed below. Compare these two tansies with Tansy Ragwort (Senecio jacobaea) – note the difference in leaves and flower structure.
In 2006 my wife and I found a nice patch of dune tansy at Schooner Cove in Pacific Rim National Park Reserve. I was working for the summer with Parks Canada and we hiked out to Schooner Cove to explore the sensitive plant communities in the dunes and the marine life in the tide pools. The dune tansy was a neat find – it is yellow listed by the BC Conservation Data Centre and appropriately enough is found only in coastal dune ecosystems in BC. Detailed information about North American status and distribution of dune tansy is available at NatureServe Explorer.
While dune tansy looks superficially like common tansy there are some key differences. Most noticeable are the ray flowers surrounding the button-like disc flowers. Common tansy lacks these ray flowers. The stem of the dune tansy is hairy and the plant has well developed basal leaves. Stem leaves are very intricately divided.
If you’re traveling in British Columbia look for these two tansies. Keep in mind that the dune tansy is grows in sandy coastal areas and that we found it blooming in July. If you discover a tansy flowering later in the year on the side of the road odds are it is a common tansy.
Read more about the historical use of Common Tansy at Common Tansy, Little Buttons of Gold.