Mystery Plant! #717

John Nelson

Posted 4/11/23

By John Nelson

 “Nemo me impune lacessit.” {In English: “Nobody messes with me and gets away with it.”]                                                                                                     –motto of the Scottish Order of the Thistle.                                       

(Photo by Linda Lee.)

Scottish history?  Tradition has it that, a long time ago, an invading band of Norwegians took off their shoes to quietly sneak up on a band of brave, defending Scots. The Norwegians ran into a big patch of bristly thistles, and of course, “ouch-ouch-ouch,” and the invasion plans were off.              

Thistles are a marvelous group of plants. Botanists place them all as members of the sunflower (or aster) family, which is a truly gargantuan group with over 20,000 species. The thistles are always characterized by tiny, elongated, tubular flowers, congested by the hundreds into massive, tight heads. The flowers are insect pollinated. Various thistle species (including the one featured here) are widely known as important food sources for butterflies, as well as bees. Of course, thistles are also characterized by spiny foliage. As well, some thistle species are valued as ornamental garden plants. Perhaps the most famous thistle of all is the species that provides us with the delicious “globe” artichoke…not to be confused with the “Jerusalem” artichoke, which is a completely different plant (a sunflower, actually).              

Our Mystery Plant is a thistle, but you will never find it in Scotland. It is, in fact, one of a series of species in North America. It grows commonly in a variety of habitats from Maine to Texas and Oklahoma, and is particularly common along the coastal plain. Residents of the eastern USA will know it as a biennial, in that it spends its first year as a rosette of leaves, then sending up a tall flowering stalk, to almost 4 feet high, in the second year. Most commonly, the plants feature wine-red flowers in their massive heads. Otherwise, yellow-flowered heads may be observed, and sometimes the two color forms are intermixed within a single population. Once the summer arrives, the colorful heads begin to produce their ripe, one-seeded fruits, each surmounted by a snowy mass of silky, plume-like bristles. Birders know thistles as a popular food source for the gold-finch; indeed, commercial thistle seed has been available for a long time now. At blooming time, the stems tend to be quite rubbery and tough, and hollow, and they are commonly purplish. The stems themselves are not prickly, but the leaves are.  At the base of each head, a prominent row of elongated bracts may be found. These bracts are very spiny themselves, and will quickly deter the most ardent flower collector, unless protected with serious gloves, and sharp clippers.                

In North America, the thistles are generally looked upon as a troublesome group, mostly because of their spiny nature. And, there are a number of introduced thistle species which are quite problematic as weeds. Nevertheless, the native thistles deserve respect as part of our natural landscapes, and should be considered as well for home gardens.

[Answer: “Bull thistle,” Cirsium horridulum]

John Nelson is the retired curator of the Herbarium at the University of South Carolina, in the Department of Biological Sciences. As a public service, the Herbarium offers free plant identifications. For more information, visit or email

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