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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 slender, elongated, tubular flowers, congested by the hundreds into massive, tight heads surrounded closely by overlapping bracts.
There are none of those flattened “ray” flowers like you see ringing the heads of zinnias or daisies. In general, the flowers are insect pollinated, and various thistle species 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 (actually not a “true” thistle, but related) 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. Our Mystery Plant is a thistle, and I was able to enter a patch of this stuff on a recent field trip in the upstate of South Carolina.
Spiny stuff! It is, in fact, one of a series of species in North America. This one is widespread, and it is likely that you have seen it growing at the edges of woods or along creeks: it pretty much occurs in every state east of the Mississippi, and also in the Midwest. The tall stems are smoothish, and the leaves are equipped with spines.
These leaves are dark green above, and show off a dense white carpet of soft hairs on the lower surface, which is one of the clues as to its identity. The plants feature numerous heads up top, each on a stalk several inches long. The flowers themselves are bright pink, and the whole head is quite attractive when in full bloom, especially on a bright, sunny day.
Blooming commences in late summer, and well into autumn. The colorful heads begin to produce their ripe, one-seeded fruits, each surmounted by a snowy mass of silky, plume-like bristles. If you are a fan of goldfinches, this is a magnet for Spinus tristis.
These fabulous birds, bright yellow and black greedily seek out the ripening achenes, before the breezes have carried them away, and it is a real treat to see a flock of them gorging themselves on the tasty seeds around the tops of the plants. In North America, there are a good many native thistles, and of course our Mystery thistle is a native. As a group, they are generally looked upon as troublesome to deal with, at least up close, 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. John Nelson is a retired botanist from the herbarium at the University of South Carolina.
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