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,
Flax contains small amounts of cyanogenic glycoside; these are nontoxic when consumed in typical amounts, but may be toxic when consumed in large quantities of such staple foods such as cassava. Typical concentrations (for example, 0.48% in a sample of defatted dehusked flaxseed meal) can be removed by special processing. The soils most suitable for flax, besides the alluvial kind, are deep loams containing a large proportion of organic matter. Flax is often found growing just above the waterline in cranberry bogs. Heavy clays are unsuitable, as are soils of a gravelly or dry sandy nature. Farming flax requires few fertilizers