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| Mexican Yellow nectaring on Texas Thistle |
As one of the most wrongly maligned and misunderstood group of wildflowers, native thistles have never been truly embraced, not even by wildscape gardeners or habitat restoration practitioners. While these plants play a significant role in our ecosystems, they have been a direct casualty of habitat loss, first by plow-based agriculture and followed by the continual development of roads and cities. Further, recent invasions of non-native, exotic thistle species and the inability to discern them from the superficially similar native species, have contributed to their unjustified reputation and ongoing demise.
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| Texas Thistle, Cirsium texanum |
Native thistles are a beautiful and important group of plants, with subtle blue-green foliage, fascinating stem and leaf architecture, and long-lasting pastel blooms that nourish many species of insects and birds. The nectar they produce is utilized by many species of bees, wasps, butterflies, moths, flies, beetles, spiders, katydids, and hummingbirds, which demonstrates the wide diversity of animals supported by native thistle flowers. In late summer and early fall, they are an essential nectar source for migrating Monarch butterflies. Their persistent seed heads provide the favorite food of goldfinches (both Lesser and American) and other songbirds such as the Carolina Chickadee, and the silky fluff attached to mature seeds is used to line their nests in the spring.
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| Silvery bracts of the Texas Thistle |
While there are many plants with spines that are erroneously called ‘thistles’, true thistles belong to the genus Cirsium. Of the 62 native species in North America, the most important species in our area are the Texas Thistle (Cirsium texanum) and the Yellow Thistle (Cirsium horridulum). The Texas Thistle, also called Southern Thistle or Gray Woolly Twintip, is an upright, unbranched or sparingly branched plant, 2 to 6.5 feet tall, with grayish-green foliage that is spiny and woolly-white below. Violet-pink to deep lavender-rose composite flower heads top the stems from April to August, and are surrounded by bracts that bear a silvery strip down the middle. Texas Thistle is also the larval host plant for the Painted Lady and Mylitta Crescent butterflies.
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| Yellow Thistle, Cirsium horridulum |
Yellow Thistle, as perhaps foreshadowed by its scientific name, has a host of other, undeserved common names such as Horrid Thistle and Terrible Thistle. It has a branching, densely hairy stem rising from a 2 foot wide basal rosette, 1 to 5.5 feet tall, with long grayish-green spiny leaves and several large flower heads. Blooming May to August, these composite flower heads are up to 3 inches wide, surrounded by a whorl of spiny, hairy, leaf like bracts, and are frequently red-purple, pink, or white instead of the namesake yellow. In the first year of growth this plant remains a low-lying rosette, and ‘bolts’ in the spring of the following year to reach its full height. Yellow Thistle is an excellent attractant for Sphinx moths and is the larval host plant for the Little Metalmark and Painted Lady butterflies.
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| Texas Thistle seed head |
It’s time to bring back our native thistles, so this fall consider planting them in your wildscape. These species have evolved with our native pollinators in our natural habitats over thousands of years. As a result, they benefit us by helping to sustain a healthy ecoweb, protecting our water quality, sequestering carbon in our soils, and adding a sublime beauty and structure to our landscapes. And that’s our epistle to the thistle!
