Linum lewisii (Linum perenne var. lewisii), known as Lewis flax, blue flax or prairie flax, is a perennial flowering plant in the family Linaceae, native to western North America from Alaska south to Baja California, and from the Pacific Coast east to the Mississippi River. It grows on ridges and dry slopes, from sea level in the north up to 3000 m altitude in the south of the species' range.
It is a slender herbaceous plant growing to 90 cm tall, with spirally arranged narrow lanceolate leaves 1–2 cm long. The flowers are pale blue or lavender to white, 1.5–3 cm diameter, with five petals.
It is commonly grown in gardens in suitable areas, especially in xeriscapes. It is extremely aggressive in favorable conditions, successfully seeding even into established lawns.
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