This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The habitat of this plant is sands by the sea. The plant has the rosette habit. The stem is short, more or less simple, branched, 3-cleft at the top. The lowest leaves are more or less round. The upper leaves are egg-shaped, oblong, 5-7-nerved, blunt. The flowers are rose-colour, more or less in a head or cyme, or in terminal, forked, round, compact tufts, with short stalks. The tube of the corolla is as long as the calyx, the lobes lance-shaped. The flowers are half as large as in Centaurium umbellatum. The plant is 2-4 in. in height, flowering in July and August, and is a herbaceous annual.
Centaurium vulgare, Raf. = C. littoralis, Fr. - The habitat of this plant is sandy seashores. The habit is as in the last. The stem is simple (1 or more). The radical leaves are narrow, numerous, spoon-shaped, crowded, the upper oblong, linear, blunt, narrowed below. The flowers are rose-colour, stalkless, between the floral leaves, in dense cymes, or corymbose, usually 3-forked, with long branches. The corolla-tube equals the calyx, and the lobes are oval, oblong, blunt. The plant is 2-6 in. high, flowering between June and September, and is a herbaceous annual.
The habitat of this plant is sandy ground. The habit is as in the last. The stem is simple, with 1 flower, or much-branched with several, acutely square in section. The leaves are egg-shaped to oblong, the upper lance-shaped. The radical leaves are few. The flowers are without bracts, rose-colour, all stalked, terminal, and in the axils, in a loose cyme or forked panicle, with a flower in each fork. The corolla tube is longer than the calyx, the lobes elliptic to oblong, lance-shaped, blunt. The lateral flowers are distant from the floral leaves. The plant is 1-6 in. high, flowering from June to September, and is a herbaceous annual.
The habitat of this plant is sandy bogs, damp sandy places. The plant has the rosette habit. The stem is slender, threadlike (hence fili-formis), forked, angled, simple or branched above, the branches more or less erect. The radical leaves are linear to lance-shaped, the stem-leaves awl-like, all stalkless. The flowers are solitary, yellow, with the parts in fours, the calyx bell-shaped, with broad, triangular, acute lobes, the corolla-lobes blunt, as long as the tube. The flower-stalks are stout and very long. The stigma is pin-headed. The capsule is round. The plant is 4-8 in. in height, flowering between July and October, and is a herbaceous annual.