“…The head of the plant being protected by thorny points: the last mentioned, however, puts forth in the middle of these points a purple blossom, which turns white with great rapidity, and is carried off by the wind… This plant, gathered before it blossoms, and beaten up and subjected to pressure, produces a juice, which, applied to the head, makes the hair grow again when it has fallen off…” from The Natural History of Pliny, pp. 299.
Thistles encompass a vast range of genus and species, so for clarification, I will refer to the family of plants that I am writing about by their botanical/binomial name.
The common thistle (Cirsium vulgare) is found in nearly all meadows and fields in Arkansas and considered a noxious weed. Though the plant does contain medicinal properties and was hailed by the Greeks as a remedy for swollen veins, there are few who actually put the knowledge gathered (over millennia) about the plant to good use.
The root of Cirsium (and its brethren) can be chewed as a remedy for toothache and has been used to expel worms in children and is an anti-inflammatory.
Because of its invasive nature, the Cirsium was banned in Great Britain and anyone who did not destroy the plants upon their land was subject to heavy penalties.
While the British railed against the plant, American Natives recognized its edibility and used another member of Cirsium (edule) as a root crop. The roots are considered sweet and like the other members of this family have medicinal value.
Today, most who do cultivate the plant do so as an ornamental for its beautiful purple bloom and its ability to draw butterflies. Few harvest the tasty root, primarily because of its thorny nature, but those who do find the taste to be similar to a potato, though some have referred to the texture as like that of a water chestnut.
For more information about various thistles or members of the Cirsium family check out the following sites:
View photos of Cirsium at ID Arkansas.
Read more about different types of thistles at Botanical.com
Read more about the Cirsium family at Wikipedia