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 old walls, cliffs, chalk-pits. The plant is erect in habit. The rootstock is woody below. The stem is round in section, hollow. The radical leaves are lance-shaped, stalked, the upper triangular, ovate to lance-shaped, stalkless, smooth, bluish-green, entire or toothed at the base. The flowers are red or white, in long terminal, panicled cymes, dense, arranged one side, with a slender spur shorter than the tube, twice as long as the ovary. The fruit is rough, narrow, ovoid, flattened. The plant is 1-2 ft. high, flowering from June to September, and is a herbaceous perennial.