The genera Sequoia and Sequoiadendron are massive trees. The genus Metasequoia, with the living species Metasequoia glyptostroboides, are smaller trees. The trees in Sequoioideae hold the record for the tallest and largest trees in the world. The tallest tree in the world is a Sequoia sempervirens, the Hyperion Tree. The largest tree in the world is a Sequoiadendron giganteum, the General Sherman Tree.
A general cooling trend beginning in the late Eocene and Oligocene reduced the northern ranges of the Sequoioideae, as did subsequent ice ages.
Sequoioideae is an ancient taxon. The first Seqoioideae, Sequoia jeholensis, was discovered in Jurassic deposits. The fossil record shows a massive expansion of range in the Cretaceous and dominance of the Arcto-Tertiary flora, especially in northern latitudes. Genera of Sequoioideae were found in the Arctic Circle, Europe, North America, and throughout Asia and Japan.
A general cooling trend beginning in the late Eocene and Oligocene reduced the northern ranges of the Sequoioideae, as did subsequent ice ages. The entire paleohistory of Sequoioideae has been a story of migration rather than adaptation. Evolutionary adaptations to ancient environments persisted in all three species despite changing climate, distribution, and associated flora.
Morphological stasis overmillennia ultimately forced these species into extremely limited ranges where they persist, though in a very vulnerable state.