Dune Tansy (Tanacetum camphoratum)

In several previous issues, I’ve written about San Francisco’s coastal dunes and some of the plant species that inhabit them. Many of the beautiful, intriguing, and rare dune species that get attention in this column are short-lived annuals that appear infrequently and require you to lie on your belly to actually get a good look (thus the term “belly plants”). Worse still, many are “comps” (members of the sunflower or daisy family, Asteraceae, formerly called Compositae), a family that causes many people to shake their heads in dismay and walk away muttering something unprintable about this group of hard-to-identify plants. Dune tansy has much more “curb appeal.” And, although a member of the daisy family, it is pretty easy to identify in the field, especially since it is the only member of the genus that you are likely to encounter in these parts and it is unlikely to be confused with any other comp.

First identified from material collected in San Francisco by Chamisso, dune tansy occurs on stable and semi-mobile coastal dunes. Its geographic range includes Alameda, Contra Costa, Del Norte, Humboldt, Los Angeles, Marin, Mendocino, San Francisco, San Mateo, Solano, and Sonoma counties. Some botanists have split off those plants occurring from Mendocino County to British Columbia as belonging to T. douglasii, although this species is not currently recognized by Jepson Interchange Online. For those of you who keep track of such things, dune tansy belongs to the mayweed tribe of the sunflower family (Anthemidae), which also includes yarrow (Achillea), dog-fennel (Anthemis), chrysanthemum, and sagebrush (Artemisia), among others.

Dune tansy is a robust, aromatic perennial herb, which forms colonies developing from underground rhizomes. Dune tansy grows two to three feet tall and has feathery leaves that might remind you of yarrow (Achillea millefolium) on steroids. Leaves are gray-green, tomentose (hairy), bi- or tri-pinnately compound, up to ten inches long and one to two inches wide. Inflorescences consist of flat-topped clusters containing three to fifteen heads of yellow flowers. Flowering occurs from June through September.

In San Francisco, dune tansy was formerly distributed as broadly as were the coastal dunes, which extended over what is now Golden Gate Park to Buena Vista Park, north to Point Lobos and south to Fort Funston. It can still be seen today near the Cliff House and Sutro Heights, at remnant dune locations overlooking the outer Sunset District (Grandview Park, Golden Gate Heights, Hawk Hill, and the Sunset Heights rock outcrop), and at Fort Funston. It has been reintroduced at Crissy Field and at Linda Mar Beach in Pacifica.

Dune tansy is an attractive herb well suited to the sandy soils found in the backyards throughout the Sunset District. It is an excellent choice for planting in gardens and, like so many of our beautiful and popular natives, doesn’t need any summer water or care once established. Tanacetum camphoratum is on the “perennials for gardens” section of Bringing Back the Natives (BBTN) list of plants that provide caterpillar food and/or nectar for up to sixty Bay Area butterfly species – www.bringingbackthenatives.net .