This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
(old Greek name, referring to the use of the plant in an ailment). Compositae. Thistle. Prickly-leaved plants (largely biennial) of bold habit and showy purple, pinkish, white or even yellowish heads, sometimes planted in wild gardens.
The thistles are botanically confused. By some authors, Cirsium is combined with Carduus, but others keep it distinct because of the plumose or feathery pappus (which is most constant on the inner florets); and this disposition is here accepted. The cirsiums are herbs or subshrubs, more or less spiny: leaves alternate, sessile, often pinnatifid: flower-heads large, mostly terminal; involucre ovoid or spherical, with many rows of imbricated often spiny-tipped scales, many-fid.; florets all tubular and alike (seldom more or less dioecious). -More than 120 species of annuals, biennials or perennials, widely spread in the northern hemisphere.
Other generic names partaking in the confused usage are Car-benia, now a synonym of Cnicus; Chamae-peuce, now a section of Cirsium; and Cnicus (which see), a genus of one species, distinguished by sterile marginal florets, pappus of ten long bristles and equal numbers of shorter ones and of horny teeth, and achene attached obliquely near the base rather than squarely on the base.
A number of the thistles are field and pasture weeds. The most penicious of these weeds is the Canada thistle, C. arvense, Scop. (Carduus arvensis, Robs.), Fig. 795. The common bull thistle or pasture thistle (Fig. 966) is a stately biennial, and very decorative. It is C. lanceolatum, Hill (Carduus lanceolatus, Linn.)- Both these species are introduced from Eu., as well as two or three others of lesser distribution in this country. There are a number of showy native species, one of which, C. muticum, Michx., (Carduus muticus, Pers.) is shown in Fig. 967. This purple-flowered species occurs in low grounds from Newfoundland to W. Va.
Fig. 966. Head of pasture or bull thistle. ( X 1/2)
Fig. 967. Cirsium muticum. (X1/2)
A few species of Cir-sium (as the genus is here defined) may be expected to occur in cultivation C. oleraceum, Scop., (Carduus oleraceus, Vill.), of Eu., has very decorative foliage, and thrives in the moister parts of a garden; the flowers are not very handsome, whitish or yellowish; 3 ft. The Chamaepeuces are sometimes grown for the large prickly spreading rosettes of leaves that are produced thefirst year, the bloom appearing the second year. They combine well with plantings made for subtropical effect: C. Casabonae, DC. (Charmepeuce Casabonae, DC. Carduus Casabonae, Linn.), has leaves deep green veined white, spiny, the flower-heads pale purple; C. Diacantha, DC. (Chamaepeuce Diocantha, DC. Carduus Diacantha, Labill.), has thick leaves shining green with silvery lines, white beneath, linear-lanceoate, the principal nerve or rib terminated by a single spine and the lateral nerves usually 2-spined, and dense clusters of purple heads; C. afrum, DC. (Charmepeuce afra, DC. Carduus afer, Jacq.), has dark green blotched white linear-lanceolate leaves tomentose beneath, and large bright purple heads; C. Sprengeri, Hort., 'a garden hybrid, perennial, with dark green white-veined spiny leaves, and white fragrant heads; C. tauricum, Hort., is probably C. Diacantha. L H. B.