| Tetracentron | |
|---|---|
| Scientific classification | |
| Kingdom: | Plantae |
| clade: | Angiosperms |
| clade: | Eudicots |
| Order: | Trochodendrales |
| Family: | Trochodendraceae |
| Genus: | Tetracentron |
| Species | |
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Tetracentron is a genus of flowering plant, the sole living species being Tetracentron sinense. It was formerly considered the sole genus in the family Tetracentraceae, though modern botanists include it in the family Trochodendraceae together with the 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, research in Molecular phylogenetics by the Angiosperm Phylogeny Group and others has shown that these two genera are not basal angiosperms, but basal eudicots.[1][2] This suggests that the absence of vessel elements is a secondarily evolved character, not a primitive one.
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,[3]; Alaska[3], Washington State, USA[3]; and Iceland,[4]. The Miocene Tetracentron atlanticum, described in 2008, is the first confirmed record of the genus in Europe. This species was described 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.[3]