Tetracentron

Taxobox
name = "Tetracentron"
regnum = Plantae
divisio = Magnoliophyta
classis = Mangnoliopsida
ordo = Trochodendrales
familia = Tetracentraceae Tiegh.
genus = "Tetracentron"
genus_authority = Oliv.
subdivision_ranks = Species
subdivision = †"Tetracentron atlanticum" †"Tetracentron piperoides"? "Tetracentron sinense"

"Tetracentron" is a genus of flowering plant, the sole living species being "Tetracentron sinense". It is also often considered the sole genus in the family Tetracentraceae, though some botanists include it in the family Trochodendraceae together with the very distinct genus "Trochodendron".

It is native to southern China and the eastern Himalaya, where it grows at altitudes of 1100-3500 m in a temperate climate; it has no widely used common name in English, though is sometimes called "spur-leaf".

It is a tree growing to 20-40 m tall. The leaves are deciduous (the "Flora of China" reporting it as evergreen is an error), borne singly at the apex of short spur shoots, each leaf dark green, broad heart-shaped, 5-13 cm long and 4-10 cm broad, with a rugose surface and a serrated margin. The spur shoots bear a one leaf each year, slowly lengthening with each subsequent year.

The flowers are inconspicuous, yellowish green, without petals, produced on slender catkins 10-15 cm long; each flower is 1-2 mm diameter. The fruit is a follicle 2-5 mm diameter, containing 4-6 seeds.

"Tetracentron" shares with "Trochodendron" the feature, very unusual in angiosperms, of lacking vessel elements in its wood. This has long been considered a very primitive character, resulting in the classification of these two genera in a basal position in the angiosperms; however, genetic research by the Angiosperm Phylogeny Group has shown it to be in a less basal position (early in the eudicots), suggesting the absence of vessel elements is a secondarily evolved character, not a primitive one.

Fossil Record

The fossil record, extending back to the Eocene, shows a much wider distribution then modern times. Fossils of this genus have been found in British Columbia, Canada,citation|last1=Pigg|first1=Kathleen|last2=Wehr|first2=Wesley|last3=Ickert-Bond|first3=Stephanie|year=2001|title="Trochodendron" and "Nordenskioldia" (Trochodendraceae) from the Middle Eocene of Washington State, U.S.A.|journal=International Journal of Plant Science|volume=162|issue=5] ; Alaska,Washington State, USA; and Iceland,citation|last1=Grímsson|first1=Friðgeir|last2=Denk|first2=Thomas|last3=Zetter|first3=Reinhard|year=2008|title=Pollen, fruits, and leaves of Tetracentron (Trochodendraceae) from the Cainozoic of Iceland and western North America and their palaeobiogeographic implications|journal=Grana|volume=73|issue=2] . The Miocene †"Tetracentron atlanticum", first described in 2008, is the first confirmed recordof the genus in Europe. This species was descripbed from pollen, fruits, and leafs found in Iceland.

Specimens from British Columbia and Washington state are found in a series of Eocene Lakes in the Okanagan Highlands region in association with several extinct "Trochodendron" species. The Paleogene species "Tetracentron piperoides" from Alaska is currently regarded as suspect due to the lack of associated fruits.

References

External links

*Flora of China: [http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200008490 "Tetracentron"] and [http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=10877 Tetracentraceae]
* [http://delta-intkey.com/angio/www/tetracen.htm Tetracentraceae] in [http://delta-intkey.com/angio/ L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants.]
* [http://www.biologie.uni-ulm.de/systax/dendrologie/Tetracsin.htm Plant Kaleidoscope: "Tetracentron"]
* [http://www.ruhr-uni-bochum.de/boga/html/Tetracentron_chinense_Foto.html Ruhr-Universität Bochum: "Tetracentron" photos]