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.
Flax is an escape from flax fields, and found in waste places. The stem is branched above, forming a corymb. The rootstock is 1-stemmed. The leaves are linear, lance-shaped, alternate. The flowers are in broad cymes or corymbs, numerous, blue. The sepals are ovate, pointed, fringed with hairs, 3-veined. The petals are scalloped. The capsule is smooth within. The plant is 1-2 ft. high, flowering between July and September, and is a herbaceous annual.