Trail Notes: Lookalike Thistles

Cirsium texanum

One of the most striking flowers blooming on the trails right now is the Texas thistle, a tall, multi-branched plant with a brilliant puff of purple at the top. A member of the sunflower family, Cirsium texanum is native to an area running from northern Mexico, throughout Texas, and up into Missouri.

In spite of its prickly reputation, Texas thistle is one of our most beneficial native plants. A larval host to painted lady butterflies, it provides nectar to assorted bees, butterflies, and other flying insects. Goldfinches, among other birds, are partial to its seeds, and collect the silky fluff to line their nests. As useful as it is beautiful, Texas thistle is extremely drought tolerant, and thus makes an all-around good addition to any pollinator garden.

Though Cirsium texanum is probably the best known of the pack, it is just one of 10 thistles native to the state. Many, especially Cirsium altissimum (tall thistle) and Cirsium engelmannii (Engelmann’s thistle), look quite similar, with their purple blooms and spiny leaves. But so, unfortunately, does an invasive, the noxious Carduus nutans, an import from Eurasia.

How to tell the difference? The Texas thistle on steroids, Cardus nutans—aka nodding thistle or musk thistle—is usually taller and invariably spinier than the native version. Its showy flowers may be attractive to pollinators, but musk thistle is extremely aggressive, capable of colonizing an entire pasture if not controlled. As Delmar Cain of the Native Plant Society of Texas has noted, “A single plant may produce 10,000 seeds, which may remain viable in the soil for 10 or more years.”

But before ripping out any purple thistles you may have growing in your yard, be sure to take a careful look. Cardus nutans can go, but Cirsium texanum deserves to stay. Whether in the garden or on the trail, it is a far more gentle and well-behaved plant, as well as a welcome host to both pollinators and birds.

Cardus nutans

Cirsium engelmannii (Engelmann’s thistle)

Cirsium altissimum (tall thistle)

– SH