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 moist rocks, mountains. The radical leaves are long-stalked, pointed, oblong, lance-shaped, the stalks slender. The flowers are large, blue, at night sweet-scented. The calyx is deeply 5-cleft, the hairs not at all straight, with some curved, appressed bristles, and narrow, acute, below, open in fruit. The ultimate flower-stalks are ascending. The limb of the corolla is longer than the tube, flat. The fruit-stalks are not so long. The style is half as long as the calyx. The nutlets are black, keeled, not rounded at the end. The plant is 4-10 in. high, flowering in July and August, and is a herbaceous perennial.