North America, Mexico, West Indies, Bermuda, Central America, South America, Eurasia, Africa, Atlantic Islands, Pacific Islands, Australia.
Genera 10–14, species ca. 260 (4 genera, 52 species in the flora).
Two subfamilies are generally recognized in Linaceae, the mostly herbaceous, temperate Linoideae Arnott (8 genera, ca. 240 species), in which all the genera in the flora area are placed, and the woody, mostly tropical Hugonoideae Reveal. Based on molecular phylogenetic analysis, J. R. McDill et al. (2009) concluded that Linaceae is a monophyletic group, as is Linoideae.
According to J. R. McDill (2009), Cliococca Babington, Hesperolinon, and Sclerolinon are nested within Linum sect. Linopsis, and collectively these are sister to Radiola; Hesperolinon and Sclerolinon are most closely related to Mexican and Central American species of Linum. McDill et al. (2009) noted that the relationships within this clade are not well-enough resolved or supported to warrant nomenclatural changes; McDill (2009) came to the same conclusion based on a much wider sample of species. The current generic circumscriptions are maintained here.
|1||Sepals 4; petals .||Radiola|
|1||Sepals 5; petals 5.||> 2|
|2||Styles 5; fruits capsules, dehiscing into 5 or 10 segments.||Linum|
|2||Styles 2–3; fruits capsules dehiscing into 4 or 6 segments, schizocarps breaking into 4 nutlets, or indehiscent.||> 3|
|3||Leaves: basal and proximal usually whorled, distal alternate or opposite; fruits capsules, dehiscing into 4 or 6 segments; styles 2–3, stigmas ± equal in width to styles; stipular glands present (exudate often red) or absent.||Hesperolinon|
|3||Leaves: proximal opposite, distal sometimes alternate; fruits schizocarps, breaking into 4 nutlets, or indehiscent; styles 2, stigmas wider than styles; stipular glands absent.||Sclerolinon|