The Genus Cirsium
Family: Asteraceae
Bristly, upright-growing herbaceous perennials from a taproot (a few species are annual, but not of the ones we grow and sell) often reaching about 2-3’ tall but as much as 5’. Bristly, thistle flowers come in many colors: reds, pinks, lavenders, purples, whites, etc.
They are incredibly attractive to a multitude of butterflies, bees, hummingbirds, and other nectar-seeking creatures. Many endangered bumblebees benefit greatly from thistles. Finches love the seeds that follow. Larval host for many butterflies. In our region you can expect the Painted Lady (Vanessa cardui), the Arizona Mylitta Crescent (Phyciodes mylitta ssp. arizonensis), and many moth species.
Thistles are spiny so avoid planting them in high-traffic areas. Many species are used as food and medicine. The roots and flowers are most often used, but sometimes the stems are also used. As food, thistles are very nutritious.
The genus, Cirsium, is derived for the Greek name for thistles. There are almost 500 species of Circium worldwide. In the Southwestern United States: Arizona and New Mexico each have 19 species of genus, California has 26 species, Nevada has 16 species, Texas has 12 species, Utah has 23 species. There are some species of Cirsium that are considered invasive. Honestly, those species usually occupy disturbed soils: roadsides, abandoned agricultural fields, ditches, etc. They don’t seem to be a big problem to the natural ecology, especially since they provide a lot to wildlife. Some ecological organizations, such as the Xerces Society, have attempted to raise awareness of the benefits of thistles, to counteract the general agricultural and home garden labeling of thistles as unwanted weeds.
Grow in full to part sun with regular water. Some species appreciate a little more shade, like the Arizona thistle, (Cirsium arizonicum). Most are very cold hardy. Plants grow much like artichokes (which they are closely related to). They grow during cool weather and start flowering late spring into summer. They may die to the ground in mid summer only to re-emerge from the roots in fall.
Graham's thistle (Cirsium grahamii), a native species that occurs in the mountains of southeastern Arizona and southwestern New Mexico. Photo by Sue Carnahan, SEINET
Arizona thistle (Cirsium arizonicum) has a flower more adapted for hummingbirds. Photo by Max Licher, SEINET.
The Cainville Thistle (Cirsium arizonicum var. bipinnatum) is a variety of the Arizona thistle that has more pink or lavender flowers, but still narrow-shaped. Photo by Patrick Alexander, SEINET
Parry's thistle (Cirsium parryi) a montane species with yellowish green flowers. Photo by Max Licher, SEINET
Field thistle (Cirsium arvense) is a non-native found in fields, roadsides, and agriculture fields. Photo by Paul Rothrock, SEINET