Flax have been domesticated just once from the wild species "Linum bienne", called pale flax. Several other species in the genus "Linum" are similar in appearance to "L. usitatissimum", cultivated flax, including some that have similar blue flowers, and others with white, yellow, or red flowers. Some of these are perennial plants, unlike "L. usitatissimum", which is an annual plant. Cultivated flax plants grow to tall, with slender stems. The leaves are glaucous green, slender lanceolate, 20–40 mm long, and 3 mm broad. The flowers are pure pale blue, 15–25 mm in diameter, with five petals. The fruit is a round,
The Different Forms of Flowers on Plants of the Same Species increase the fertility of this common plant. The same thing was found to occur in the primrose, as well as in flax (Linum perenne), lungworts (Pulmonaria), and a host of other plants, including the American partridge-berry (Mitchella repens). These are called dimorphic heterostyled plants. Still more extraordinary is the case of the common loosestrife (Lythrum salicaria), which has both stamens and styles of three distinct lengths, each flower having two sets of stamens and one style, all of different lengths, and arranged in three different ways: These flowers can be fertilised in eighteen distinct ways, necessitating a vast number of