Sequoioideae (redwoods) is a subfamily of coniferous trees within the family Cupressaceae. It is most common in the coastal forests of Northern California.
Video Sequoioideae
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.
Maps Sequoioideae
Taxonomy and evolution
Multiple studies of both morphological and molecular characters have strongly supported the assertion that the Sequoioideae are monophyletic.
Most modern phylogenies place Sequoia as sister to Sequoiadendron and Metasequoia as the out-group. 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.
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. 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.
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.
Range
California, USA
- The native habitat of Sequoiadendron giganteum trees is only on the western slopes of the Sierra Nevada range of California.
- The native habitat of Sequoia sempervirens trees is only in the Northern California coastal forests ecoregion, on the Northern California coast and several miles into Oregon.
China
- Metasequoia glyptostroboides trees are so rare they were thought to be extinct, until rediscovered by a Chinese forester in 1943. They were found on mountainous slopes in remote parts of the Hubei region of China.
Paleontology
Sequoioideae is an ancient taxon, with the oldest described Sequoioideae species, Sequoia jeholensis, recovered from Jurassic deposits. A genus Medulloprotaxodioxylon, reported from the late Triassic of China supports the idea of a Norian origin.
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. 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
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. 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."
See also
- Cloud forest
- Fitzroya, the Alerce tree of South America
- List of superlative trees
References
Bibliography and links
- "About the trees". National Park Service. Retrieved 10 January 2014.
- "A few basic facts about Redwoods, and Parks". National Park Service. Retrieved 10 January 2014.
- "Calaveras Big Trees Association". Retrieved 10 January 2014.
- Hanks, Doug (2005). "Crescent Ridge Dawn Redwood Preserve". Retrieved 10 January 2014.
- de:Liste der dicksten Mammutbäume in Deutschland. List of Large Giant Redwoods in Germany
- IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. Downloaded on 10 January 2014.
- James Donald, John Rubin (directors) (2009). Climbing Redwood Giants (film). National Geographic.
- "Big trees". Notes from the Field tv. 6 minutes in. PBS. Retrieved 10 January 2014.
Source of article : Wikipedia
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