Sequoioideae

Sequoioideae
Temporal range: Jurassic to Recent
Sequoiadendron giganteum
Scientific classification
Kingdom: Plantae
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Cupressaceae
Subfamily: Sequoioideae
Genera

Sequoioideae (redwoods) is subfamily of coniferous trees within the family Cupressaceae.[1] It is most common in the coastal forests of Northern California.

Description

The three redwood subfamily genera are Sequoia and Sequoiadendron of California and Oregon, United States; and Metasequoia in China. The redwood species contains the largest and tallest trees in the world. These trees can live thousands of years. This is an endangered subfamily due to habitat losses from fire ecology suppression, logging, and air pollution.

Only two of the genera, Sequoia and Sequoiadendron, are known for massive trees. Metasequoia, with the living species Metasequoia glyptostroboides, are much smaller.

Taxonomy and evolution

Multiple studies of both morphological and molecular characters have strongly supported the assertion that the Sequoioideae are monophyletic.[2][3][4][5]

Most modern phylogenies place Sequoia as sister to Sequoiadendron and Metasequoia as the out-group.[3][5][6] However, Yang et al. went on to investigate the origin of a peculiar genetic artifact of the Sequoioideae—the polyploidy of Sequoia—and generated a notable exception that calls into question the specifics of this relative consensus.[5]

Evidence for reticulate evolution in Sequoioideae

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.[7] Within the gymnosperms however it is quite rare. Sequoia sempervirens is hexaploid (2n= 6x= 66). To investigate the origins of this polyploidy Yang et al. used two single copy nuclear genes, LFY and NLY, to generate phylogenetic trees. Other researchers have had success with these genes in similar studies on different taxa.[5]

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.

Yang et al. found that Sequoia was clustered with Metasequoia in the tree generated using the LFY gene, but with Sequoiadendron in the tree generated with the NLY gene. Further analysis strongly supported the hypothesis that Sequoia was the result of a hybridization event involving Metasequoia and Sequoiadendron. Thus, Yang et al. hypothesize that the inconsistent relationships among Metasequoia, Sequoia, and Sequoiadendron could be a sign of reticulate evolution (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.[6]

Range

California, USA

China

Paleontology

Sequoioideae is an ancient taxon, with the oldest described Sequoioideae species, Sequoia jeholensis, recovered from Jurassic deposits.[8]

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. [9] A general cooling trend beginning in the late Eocene and Oligocene reduced the northern ranges of the Sequoioideae, as did subsequent ice ages.[10] 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.

Conservation

Young but already tall redwood trees (Sequoia sempervirens) in Oakland, California.

The entire subfamily is endangered. The IUCN Red List Category & Criteria assesses Sequoia Sempervirens as Endangered (A2acd), Sequoiadendron giganteum as Endangered (B2ab) and Metasequoia glyptostroboides as Endangered (B1ab).

Introduced range

The two California redwood species, since the early 19th century, and the Chinese redwood species since 1948, have been cultivated horticulturally far beyond their native habitats. They are found in botanical gardens, public parks, and private landscapes in many similar climates worldwide. Plantings outside their native ranges particularly are found in California, the coastal Northwestern and Eastern United States, areas of China, Germany, the United Kingdom, Australia and near Rotorua New Zealand.[11] They are also used in educational projects recreating the look of the megaflora of the Pleistocene landscape.

Cultural impact

John Steinbeck wrote about the redwood, "The redwoods, once seen, leave a mark or create a vision that stays with you always. No one has ever successfully painted or photographed a redwood tree. The feeling they produce is not transferable. From them comes silence and awe. It's not only their unbelievable stature, nor the color which seems to shift and vary under your eyes, no, they are not like any trees we know, they are ambassadors from another time."[12]

See also

References

  1. ↑ "Sequoioideae". Wikispecies. 24 May 2009. Retrieved 2010-07-10.
  2. ↑ Brunsfeld, Steven J.; Soltis, Pamela S.; Soltis, Douglas E.; Gadek, Paul A.; Quinn, Christopher J.; Strenge, Darren D.; Ranker, Tom A. (1994). "Phylogenetic relationships among the genera of Taxodiaceae and Cupressaceae: evidence from rbcL sequences". Systematic Botany. 19 (2).
  3. 1 2 Gadek, P.A.; Alpers, D.L.; Heslewod, M.M.; Quinn, C.J. (2000). "Relationships Within Cupressaceae Sensu Lato: A Combined Morphological and Molecular Approach". American Journal of Botany. 87 (7): 1044–57. PMID 10898782. doi:10.2307/2657004.
  4. ↑ Takaso, T.; Tomlinson, P.B. (1992). "Seed cone and ovule ontogeny in Metasequoia, Sequoia and Sequoiadendron (Taxodiaceae-Coniferales)". Botanical Journal of the Linnean Society. 109: 15–37. doi:10.1111/j.1095-8339.1992.tb00256.x.
  5. 1 2 3 4 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: 452–470. PMID 22609823. doi:10.1016/j.ympev.2012.05.004.
  6. 1 2 Mao, K.; Milne, R.I.; Zhang, L.; Peng, Y.; Liu, J.; Thomas, P.; Mill, R.R.; Renner, S.S. (2012). "Distribution of Living Cupressaceae Reflects the Breakup of Pangea". Proceedings of the National Academy of Sciences. 109 (20): 7793–7798. PMC 3356613 Freely accessible. PMID 22550176. doi:10.1073/pnas.1114319109.
  7. ↑ Soltis, D.E.; Buggs, R.J.A.; Doyle, J.J.; Soltis, P.S. (2010). "What we still don't know about polyploidy". Taxon. 59.
  8. ↑ Ahuja M. R. and D. B. Neale. 2002. Origins of polyploidy in coast redwood (Sequoia sempervirens) and relationship of coast redwood (Sequoia sempervirens) to other genera of Taxodiaceae. Silvae Genetica 51: 93–99.
  9. ↑ Chaney, Ralph W. (1950). "Revision of Fossil Sequoia and Taxodium in Western North America Based on the Recent Discovery of Metasequoia". Transactions of the American Philosophical Society. Philadelphia. 40 (3): 172–236. ISBN 1422377059. doi:10.2307/1005641. Retrieved 1 January 2014.
  10. ↑ Jagels, Richard; Equiza, María A. (2007). "Why did Metasequoia disappear from North America but not from China?". Bulletin of the Peabody Museum of Natural History. 48 (2): 281–290. doi:10.3374/0079-032x(2007)48[281:wdmdfn]2.0.co;2.
  11. ↑ "Kia Ora – Welcome to The Redwoods Whakarewarewa Forest". Rotorua District Council. Retrieved 10 November 2011.
  12. ↑ Steinbeck, John (1961) Travels with Charley: In Search of America.Viking: New York. Page 182.
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