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 walls and dry sandy places. The habit is prostrate. The stems are spreading, branched, slender, brittle. There are no barren shoots. The leaves are 6 in a whorl, or the lower 4 in a whorl, narrow, linear, blunt-pointed, bent-back at length, the margins rough, with forwardly-directed prickles. The flowers are few, greenish-white, in small, forked, axillary and terminal cymes, panicled, with spreading branches, nearly at right angles to the stalks. The fruit is small, tubercled, black. The plant is 6-12 in. high, flowering in June and July.
The habitat of this plant is moist rocks in mountain districts in North Britain. The habit is erect. The stems are rigid, tufted, leafy, with few branches above. The rootstock is creeping. The plant is smooth to downy, black when dry. The leaves are 4 in a whorl, lance-shaped, smooth, downy, 3-nerved. The flowers are large, white, in terminal and axillary, compact, many-flowered, panicled cymes, the branches more or less erect. The bracts are ovate. The fruit is covered with hooked bristles. The fruit-stalks are erect. The plant is 6-24 in. high, flowering from June to August, and is a herbaceous perennial.