Centaurea

Centaurea, a palæarctic genus of Compositæ, containing about two hundred species, all herbaceous annual and perennial, of which five or six are natives of Britain. The species most familiar, on account of its beauty, is the blue C. cyanus (see CORN-FLOWER), which is sometimes sown as an annual; while its larger perennial ally, C. montana, with white or purple ray florets, is a familiar denizen of old-fashioned gardens; C. americana is a showy lilac-purple annual (3 or 4 feet); while the oriental Sweet Sultan (C. moschata) and Yellow Sultan (C. amberboa) are also not uncommon; the latter two being often sold under the name of Amberboa. Among perennials, the large, downy C. babylonica, with yellow flowers, is often cultivated; also C. ragusina and C. candidissima, of which the silver-white pinnate leaves furnish an admired contrast to bright-coloured bedding-plants. Several species (C. calcitrata, &c.) bear the name of Star-thistle, from their spiny involucre. Some are common wayside weeds, often troublesome in pastures, notably C. nigra, the Common or Black Knapweed, also called Horse Knot in Scotland; and the closely allied C. Scabiosa. The flowers or roots of several species were formerly used in dyeing, and the astringent roots employed by herbalists.