There are five other British species of Centaurea, of which several are rare or extremely local in their distribution. The more frequent species are:—
I. Black Knapweed (C. nigra). Leaves rough, entire or lobed, the lower ones with stalks. The heads large and globose, as much as an inch and a half in diameter. Involucral scales circular, brown, toothed. Florets purple. Common in meadows and pastures. June to September.
II. Greater Knapweed, or Hard Heads (C. scabiosa). The leaves are deeply pinnate, like the lower ones of Bluebottle. Heads as much as two inches diameter. Involucral scales cottony, with dark brown, almost black, margin, and paler fringe. Florets rich purple. Waste places. July to September.
Round-leaved Mallow (Malva rotundifolia).
The Round-leaved or Dwarf Mallow is not so well known as the Common Mallow (M. sylvestris) , though it is nearly as common. Its flowers are small, and not nearly so conspicuous as those of sylvestris. Like that plant it is found growing by the wayside and on waste places where garden refuse, etc., is dumped. Our three species of Malva are all perennials, and all possess tough fibrous stems. Those of rotundifolia are downy, and lie along the ground and bear many lobed, often toothed, leaves, whose general outline is circular. The flowers are clustered in the axils, and consist of a five-parted calyx, to which is attached a kind of involucre of three bracts, and five distant petals, their tips with a central notch. There are ten
styles, the inner surfaces of which are stigmatic; they curl about in various directions, mingling with the numerous anthers, and so ensuring self-fertilization. The fruit consists of a large number of one-seeded carpels arranged in a circle, but easily becoming detached after ripening. Flowers June to September.
The other species are:—
