THISTLE, a name, as generally employed, of vague application, being given to almost any herbaceous plant that is of a spiny character. More strictly, it is applied to the species of Carduus. These are Composite herbs with very spiny leaves, and similar bracts surrounding a head of purplish-white, tubular, five-parted flowers seated on a pitted and hairy receptacle. The anthers have appendages both at the apex and at the base, and the style has a ring of hairs at the point of bifurcation of the two stigmas. The fruit is surmounted by a tuft of silky-white hairs. The species, chiefly natives of Europe and Western Asia, are numerous, and some are of great beauty, though, not unnaturally, looked on with disfavour by the farmer. The blessed thistle is Carduus benedictus; Lady's thistle, the leaves of which are spotted with white, is C. marianus. The common C. lanceolatus seems to be the most suitable prototype for the Scots thistle, though that honour is also conferred on an allied plant Onopordon acanthium, the cotton thistle, remarkable for its covering of white down, a doubtful native, and on other species. The carline thistle is Carlina vulgaris, a member of the same family, as is also the sow-thistle, Sonchus oleraceus. The great objection to thistles from an agricultural point of view resides in the freedom with which they produce seed, and in the vigour of their underground growth, which makes their uprooting a matter of difficulty. Partial uprooting may, indeed, in the case of the perennial species, increase the mischief, for each fragment left behind may grow into a distinct plant. Annual species might be kept in check were they cut down before the flowers appear, but unless all the cultivators in a particular district co-operate the efforts of individuals are of little avail. The Artichoke (q.v.), Cynara scolymus, and Cardoon (q.v.) are very near allies of the thistles. The Safflower, Carlhamus, another thistle, yields a serviceable dye; the Burdock, Arclium lappa, a member of the same family, has an edible root; and numerous allied species have medicinal properties.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)