There will always be thistle, said the late US Poet Laureate Maxine Kumin in one of her poems, because "Sheep will not eat it / nor horses nor cattle / unless they are starving." She described it "choking the sweet grass / defeating the clover," and pricking the hands with its spines.
Okay, I guess thistles are not everyone's favorite wildflower, but I've always liked them. I'm not a farmer, so it's easy for me to say. I like them because they're pretty, they remind me of the vast Minnesota prairie, and they're like grocery stores for goldfinches.
Members of the sunflower family, thistles thrive in almost any environment except deep woods: open fields, sand and gravel pits, vacant lots, roadsides, and the edges of wetlands. The US has more than 200 species, growing from two to ten feet high and bearing pink, purple, white, or yellow blooms. The flowers are large; most thistle plants only flower once in a lifecycle, so a lot of energy goes into producing seed in that one bloom. Some species produce 4,000 to 10,000 seeds per plant.
North America has native and non-native thistles. The thistle's bad reputation is mostly due to the weedy and invasive nature of several non-native species. They compete with crops, and their deep tap roots make them difficult to eradicate. They're also very prickly. Native species, on the other hand, have stems that range from hairy to slightly prickly. Non-native thistle species in Minnesota include the bull thistle, the musk thistle, and the Canada thistle (which is misnamed, since it was brought from Europe to North America). So hated is the Canada thistle that many states have put it on their Prohibited Noxious Weed list.
Non-native thistles get a lot of people's goats. (Goats will eat thistles, though they save them for last.) Unfortunately, native thistles suffer as a result. According to the Xerces Society, native thistles are accidently targeted for removal along with non-native ones, putting several species at risk of extinction. The Society's scientists point out that, in some regions, monarch butterflies visit native thistles more than any other wildflower during their migration. Other butterflies and bees do not discriminate. Whether native or introduced, thistles are a favorite food for pollinating insects and many birds.
The thistle's biggest fan is the American goldfinch. Goldfinches rely heavily on thistle plants for food and use thistledown in their nests. Unlike most songbirds, goldfinches rarely eat insects or feed them to their babies. They are late breeders, building nests in late June and early July and raising nestlings in late summer when thistle seed heads are abundant. Upside-down goldfinches are a common sight as they bend thistle stalks over completely and cling to flowers to peck at the seed heads.
Native thistles also include the field thistle and the pasture thistle. Also native, but less widespread, is the swamp thistle. With all the current threats to pollinators, including habitat loss, pollution, climate change, and light pollution, native thistles deserve some love.