| Sequoioideae | |
|---|---|
 | |
| Redwood Highway, CaliforniaSequoia sempervirens | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnospermae |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Cupressales |
| Family: | Cupressaceae |
| Subfamily: | Sequoioideae |
| Genera | |
Sequoioideae, commonly referred to asredwoods, is asubfamily ofconiferous trees within thefamilyCupressaceae, that range in thenorthern hemisphere. It includes thelargest and tallest trees in the world. The trees in thesubfamily are amongst the most notable trees in the world and are commonornamental trees. Thesubfamily reached its peak of diversity during the earlycenozoic.
The three redwood subfamilygenera areSequoia from coastalCalifornia andOregon,Sequoiadendron from California'sSierra Nevada, andMetasequoia inChina. The redwood subfamily contains the largest and tallest trees in the world. These trees can live for thousands of years. Threats include logging, fire suppression,[1] illegal marijuana cultivation, andburl poaching.[2][3]
Only two of the genera,Sequoia andSequoiadendron, are known for massive trees. Trees ofMetasequoia, from the single living speciesMetasequoia glyptostroboides, are deciduous, grow much smaller (although are still large compared to most other trees) and can live in colder climates.[citation needed]
Multiple studies of both morphological and molecular characters have strongly supported the assertion that the Sequoioideae aremonophyletic.[4][5][6][7] Most modernphylogenies placeSequoia as sister toSequoiadendron andMetasequoia as the out-group.[5][7][8] However, Yanget al. went on to investigate the origin of a peculiar genetic component in Sequoioideae, thepolyploidy ofSequoia—and generated a notable exception that calls into question the specifics of this relative consensus.[7]
A 2006 paper based on non-molecular evidence suggested the following relationship among extant species:[9]
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A 2021 study using molecular evidence found the same relationships among Sequoioideae species, but found Sequoioideae to be the sister group to theAthrotaxidoideae (a superfamily presently known only fromTasmania) rather than toTaxodioideae. Sequoioideae and Athrotaxidoideae are thought to have diverged from each other during theJurassic.[10]
Reticulate evolution refers to the origination of a taxon through the merging of ancestor lineages.Polyploidy has come to be understood as quite common in plants—with estimates ranging from 47% to 100% of flowering plants and extantferns having derived from ancient polyploidy.[11] Within the gymnosperms however it is quite rare.Sequoia sempervirens ishexaploid (2n= 6x= 66). To investigate the origins of this polyploidy Yang et al. used two single copynuclear genes,LFY and NLY, to generatephylogenetic trees. Other researchers have had success with these genes in similar studies on different taxa.[7]
Several hypotheses have been proposed to explain the origin ofSequoia'spolyploidy:allopolyploidy byhybridization betweenMetasequoia and some probably extincttaxodiaceous plant;Metasequoia andSequoiadendron, or ancestors of the two genera, as the parental species ofSequoia; andautohexaploidy, autoallohexaploidy, or segmental allohexaploidy.[citation needed]
Yang et al. found thatSequoia was clustered withMetasequoia in the tree generated using the LFY gene but withSequoiadendronin the tree generated with the NLY gene. Further analysis strongly supported the hypothesis thatSequoia was the result of ahybridization event involvingMetasequoia andSequoiadendron. Thus, Yang et al. hypothesize that the inconsistent relationships amongMetasequoia,Sequoia, andSequoiadendron could be a sign ofreticulate evolution byhybrid 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 theJurassic) make resolving the specifics of when and howSequoia originated once and for all a difficult matter—especially since it in part depends on an incomplete fossil record.[8]
Sequoioideae is an ancienttaxon, with the oldest described Sequoioideae species,Sequoia jeholensis, recovered fromJurassic deposits.[12][13] The fossil woodMedulloprotaxodioxylon, reported from the late Triassic of China, resemblesSequoiadendron giganteum and may represent an ancestral form of the Sequoioideae; this supports the idea of a Late TriassicNorian origin for this subfamily.[14]
The fossil record shows a massive expansion of range in theCretaceous and dominance of theArcto-Tertiary Geoflora, especially in northern latitudes. Genera of Sequoioideae were found in theArctic Circle, Europe, North America, and throughout Asia and Japan.[15] A general cooling trend beginning in the lateEocene andOligocene reduced the northern ranges of the Sequoioideae, as did subsequent ice ages.[16] 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.[citation needed]
The extinct genusAustrosequoia, known from the Late Cretaceous-Oligocene of the Southern Hemisphere, including Australia and New Zealand, has been suggested as a member of the subfamily.[17]
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In 2024, it was estimated that there were about 500,000 redwoods in Britain, mostly brought as seeds and seedlings from the US in theVictorian era.[18] The entire subfamily isendangered. TheIUCN Red List Category & Criteria assessesSequoia sempervirens as Endangered (A2acd),Sequoiadendron giganteum as Endangered (B2ab) andMetasequoia glyptostroboides as Endangered (B1ab). In 2024 it was reported that over a period of two years about one-fifth of all giant sequoias were destroyed in extreme wildfires in California.[19]
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