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.
This plant is naturalized, and grows on rocky banks, waste places. The plant has the lily habit. The stem is leafy below. The bulb is large, with stalked bulbils or offsets, and compound. The leaves are keeled, linear, in two rows, folded, with rough edges. The sheaths are cylindrical. The scape is stout. The spathe has a flattened, long beak, falling off, entire. The flowers are numerous, in a round, compact umbel, pale-purple or greenish-white, on unequal stalks. The perianth is white or greenish, the keel of the outer segments roughish. The stamens project, and the anther-bearing point has 3-pointed filaments as long as the entire part. The ovary is rounded. The plant is 3-4 ft. high, flowering in July and August, and is a herbaceous perennial.
The habitat of this plant is rocky ledges, mountain cliffs. The habit is the lily habit. The stem and leaves arise separately from the rootstock. The stem is round. The sheaths of the bulb are numerous and loose. The radical leaves are semi-cylindrical, 3-angled, bent inwards. The stem-leaves are not so long, swollen below, sheathing, short. The flowers are white, with reddish lines within, solitary. The perianth-segments are inversely ovate to oblong. The capsule is 3-sided, 3-valved above. The seeds are reddish-brown till they are ripe. The plant is 4-8 in. high, flowering in May and June, and is a herbaceous perennial.