Tilia is a genus of about 30 species of trees native throughout most of the temperate Northern Hemisphere. Commonly called lime trees in the British Isles, they are not closely related to the lime fruit. Other names include linden and basswood. The greatest species diversity is found in Asia, and the genus also occurs in Europe and eastern North America. Under the Cronquist classification system, this genus was placed in the family Tiliaceae, but genetic research by the Angiosperm Phylogeny Group has resulted in the incorporation of this genus into the Malvaceae.
Tilia species are large deciduous trees, reaching typically 20 to 40 metres (66 to 130 ft) tall, with oblique-cordate leaves 6 to 20 centimetres (2 to 8 in) across. The exact number of species is subject to considerable uncertainty, as many or most of the species will hybridise readily, both in the wild and in cultivation.
Tilioideae is a botanical name at the rank of subfamily. It was formerly considered a large group, placed at family rank and called Tiliaceae.
Within the framework of the APG II system, an extended family Malvaceae is recognized. This is formed by uniting the core Malvales of the Cronquist system - Bombacaceae, Malvaceae sensu stricto, Sterculiaceae and Tiliaceae. This Malvaceae sensu lato contains a clade of only 2 or 3 living genera which include Tilia (linden, basswood), the clade consequently becoming the Tilioideae.
Apart from the namesake genus Tilia and Craigia, according to the AP-Website the Tilioideae seem to contain also the genus Mortoniodendron. Most other genera of the "Tiliaceae" fall into two other subfamilies of Malvaceae, the Brownlowioideae and Grewioideae.