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Paleoendemism in Redwoods
Coast redwoods (Sequoia sempervirens) are the only remaining species in the genus Sequoia, a group which once spanned much of the Northern Hemisphere. The species currently ranges from the central coast of California to the edge of southern Oregon, this species is only one example of paleoendemics within this region due to the long ranging stability of its foggy coastal climate. Although now geographically restricted, Sequoia and the other three members of the subfamily Sequoioideae, were at one point widely distributed throughout North America and Eurasia.

Most of the understanding of the historic range of Sequoia is from evidence in the fossil record. While the redwood family, Taxodiaceae, can be traced to the Permian period, the first morphologically distinguishable records of Sequoia were discovered in France and Manchuria dating back to the Jurassic period. During the Cenozoic, Sequoia was nearly circumpolar in its distribution, but this range began to shrink approximately 30 million years ago

As the climate began to warm, grasslands began dominating much of North America, restricting Sequoia to regions with high summer moisture. By the transition to the Miocene, the range of the Sequoia became similar to what is seen today, with the species becoming restricted to the western coastal forests as the valley became drier and inhospitable; however populations remained on the wettest western slopes of the Sierras and Cascades into the Holocene. These populations contracted following a drying period in the Neogene as seasonal rainfall shifted and the seasons became more extreme following the tectonic activity of the time which uplifted these ranges. (Look into Axelrod 1977/1978)

Metasequoia
The Dawn Redwood (Metasequoia glyptostroboides) is the only surviving species of the four known Metasequoia, and one of only three surviving Redwood species. Although reduced to a single native population within in China's Lichuan County, during the Late Cretaceous the species was widely distributed across North America and Eurasia.The fossil record shows the genus persisting in a diverse array of climates, including the harsh cold of the polar latitudes. Many of the fossils in the high northern latitudes and mid-latitudes during the Cenozoic which were identified as Sequoia have been properly identified as Metasequoia following its rediscovery in 1941. The drastic reduction in the range of Metasequoia began during the Miocene, during which time it began to withdraw from the polar regions toward Southern China where it is found today. The cause of this dramatic range reduction has been theorized to increased competition from Pinaceae and the transition toward an arid and unsuitable climate through much of its historic range. The fossil record suggests that there have been no phenotypic changes to Metasequoia since the Cretaceous.

Other examples of paleoendemic plants:
Ginkgo biloba

Quercus durata

Pinus torreyana

Australian Acacia (this is only some species, but the paper doesn't say which ones? Probably should remove.)

Araucaria bidwillii