(flax), a family of dicotyledonous plants, including grasses, subshrubs, and shrubs. The simple leaves, which are alternate or rarely opposite, have small stipules or, rarely, are exstipulate. The flowers are bisexual, regular, and five-parted (rarely four-parted). There are six genera, with approximately 250 species, found primarily in temperate and subtropical regions; some species, however, are found the tropics of the Old World. The families Hugoniaceae, Ixonanthaceae, and Humiriaceae are often included in the Linaceae. Using this classification, the family Linaceae has more than 25 genera, comprising approximately 500 species, and includes trees and lianas. These 25 genera are distributed from the tropics to the temperate regions of both hemispheres. There are two genera in the USSR— Linum and Radiola, with the latter having one species.