Trochodendron
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| Trochodendron aralioides Siebold & Zucc. |
Trochodendron aralioides is a flowering plant, the sole species in the genus Trochodendron. It is also often considered the sole species in the family Trochodendraceae, though some botanists include the very distinct genus Tetracentron in the same family. Trochodendron is native to southern Japan, southern Korea and Taiwan; it has no widely used common name in English, though is sometimes colloquially called "wheel tree".
It is an evergreen tree or large shrub growing to 20 m tall. The leaves are borne in tight spirals at the apex of the years' growth, each leaf leathery dark green, simple broad lanceolate, 6-14 cm long and 3-8 cm broad, with a crenate margin. The flowers are produced 10-20 together in a racemose cyme 5-13 cm diameter; each flower is 15-18 mm diameter, yellowish green, without petals, but with a conspicuous ring of 40-70 stamens surrounding the 4-11 carpels. The fruit is 2 cm diameter, woody, star-shaped, composed of 4-11 follicles, each follicle containing several seeds.
Trochodendron shares with Tetracentron 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.
