Cladistic tree A 2006 paper based on non-molecular evidence suggested the following relationship among extant species: A 2021 study using molecular evidence
found the same relationships among Sequoioideae species, but found Sequoioideae to be the sister group to the Athrotaxidoideae (a superfamily presently known only from Tasmania) rather than to Taxodioideae.
hypothesize that the inconsistent relationships among Metasequoia, Sequoia, and Sequoiadendron could be a sign of reticulate evolution by hybrid speciation (in which two species
hybridize and give rise to a third) among the three genera.
However, the long evolutionary history of the three genera (the earliest fossil remains being from the Jurassic) make resolving the specifics of when and how Sequoia originated
once and for all a difficult matter—especially since it in part depends on an incomplete fossil record.
 Evolutionary adaptations to ancient environments persist in all three species despite changing climate, distribution, and associated flora, especially the specific demands
of their reproduction ecology that ultimately forced each of the species into refugial ranges where they could survive.
 Several hypotheses have been proposed to explain the origin of Sequoia’s polyploidy: allopolyploidy by hybridization between Metasequoia and some probably extinct taxodiaceous
plant; Metasequoia and Sequoiadendron, or ancestors of the two genera, as the parental species of Sequoia; and autohexaploidy, autoallohexaploidy, or segmental allohexaploidy.
 Only two of the genera, Sequoia and Sequoiadendron, are known for massive trees.
Trees of Metasequoia, from the single living species Metasequoia glyptostroboides, are deciduous, grow much smaller (although are still large compared to most other trees)
and can live in colder climates.
Polyploidy has come to be understood as quite common in plants—with estimates ranging from 47% to 100% of flowering plants and extant ferns having derived from ancient polyploidy.
 A genus Medulloprotaxodioxylon, reported from the late Triassic of China supports the idea of a Norian origin.
The redwood species contains the largest and tallest trees in the world.
Wan, Mingli; Yang, Wan; Tang, Peng; Liu, Lujun; Wang, Jun (2017). “Medulloprotaxodioxylon triassicum gen. Et sp. Nov., a taxodiaceous conifer wood from the Norian (Triassic) of northern Bogda Mountains, northwestern China”. Review of Palaeobotany and
Palynology. 241: 70–84. doi:10.1016/j.revpalbo.2017.02.009. ^ “Prescribed Fire at Redwood National and State Parks – Redwood National and State Parks (U.S. National Park Service)”. ^ “The Threats to the Redwoods”. ^ “Why redwood burl poaching is so
destructive”. Christian Science Monitor. 5 March 2014. ^ Kurland, Justin; Pires, Stephen F; Marteache, Nerea (2018). “The spatial pattern of redwood burl poaching and implications for prevention”. Forest Policy and Economics. 94: 46–54. doi:10.1016/j.forpol.2018.06.009.
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rbcL Sequences”. Systematic Botany. 19 (2): 253. doi:10.2307/2419600. JSTOR 2419600. ^ Jump up to:a b Gadek, P.A.; Alpers, D.L.; Heslewod, M.M.; Quinn, C.J. (2000). “Relationships Within Cupressaceae Sensu Lato: A Combined Morphological and Molecular
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Journal of the Linnean Society. 109: 15–37. doi:10.1111/j.1095-8339.1992.tb00256.x. ^ Jump up to:a b c d Yang, Z.Y.; Ran, J.H.; Wang, X.Q. (2012). “Three Genome-based Phylogeny of Cupressaceae s.l: Further Evidence for the Evolution of Gymnosperms
and Southern Hemisphere Biogeography”. Molecular Phylogenetics and Evolution. 64 (3): 452–470. doi:10.1016/j.ympev.2012.05.004. PMID 22609823. Photo credit: https://www.flickr.com/photos/joeshlabotnik/497305666/