Modern understanding of the phylogeny and taxonomy of genus Linum L. and flax (Linum usitatissimum L.)

The flax family (Linaceae DC. ex Perleb.) formed 95-105 million years ago from the family Malpighiaceae Juss. and includes 300-330 species, united in two subfamilies - Hugonioideae Arn. and Linoideae (DC. ex Perleb.) Arn. First species of Linoideae became isolated from the subfamily Hugonioideae 46-51 million years ago in Southeast Asia. The species of the genus Linum L. appeared in Eurasia 41-46 million years ago and had a yellow color of corolla. Blue flowering species became isolated 32-29 million years ago in Central Asia in the conditions of cold weather and global climate aridity. The author's concept of the separation blue flowering species from the red flowering ones based on the analysis of intermediate color corolla forms of flax is proposed. The known classifications of the genus Linum with 100 to 230 different species are differed with excess synonymy because of different understanding of the species nature. Different interpretations of the species concepts led to identification of new flax types with a slightly different morphology or growing in isolated areas. Awareness of the imperfections of this approach has caused the active revision of the genus Linum taxonomy and species L. usitatissimum. Intraspecific classification of L. usitatissimum, proposed by A. Diederrichsen and K. Richards (2003), is currently the most logical. Previously described as a separate species: fiber flax (L. usitatissimum), crown flax (L. crepitans), common flax (L. humile) and several others are combined into one polymorphic species L. usitatissimum, which includes four varieties’ groups: wild and semi-wild flax (convar. crepitans); long-fibred flax (convar. elongatum); large-seeded flax (convar. mediterraneum); intermediate flax (convar. usitatissimum). This classification is best suited for flax breeding. Selecting smaller taxa does not make sense because of the wide variability of morphotypes and ecotypes of existing varieties.