Trochodendron aralioides
Encyclopedia
Trochodendron aralioides, sometimes colloquially called "wheel tree", is a flowering plant
and the sole living species in the genus Trochodendron
, which also includes several extinct species. It was also often considered the sole species in the family Trochodendraceae
, though botanists now include the distinct genus Tetracentron
in the same family. T. aralioides is native to Japan
, southern Korea
and Taiwan
.
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 flower
s 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 stamen
s surrounding the 4-11 carpels. The fruit
is 2 cm diameter, woody, star-shaped, composed of 4-11 follicles
, each follicle containing several seed
s.
Trochodendron aralioides shares with Tetracentron the very unusual feature in angiosperms
, of lacking vessel element
s 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.
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
and the sole living species in the genus Trochodendron
Trochodendron
Trochodendron is a genus of flowering plants with one living species, Trochodendron aralioides, and six extinct species known from the fossil record...
, which also includes several extinct species. It was also often considered the sole species in the family Trochodendraceae
Trochodendraceae
Trochodendraceae is a family of flowering plants with two living genera found in southeast Asia. The two living species share the feature of secondary xylem without vessels, which is quite rare in angiosperms...
, though botanists now include the distinct genus Tetracentron
Tetracentron
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...
in the same family. T. aralioides is native to Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, southern Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
and Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
.
It is an evergreen
Evergreen
In botany, an evergreen plant is a plant that has leaves in all seasons. This contrasts with deciduous plants, which completely lose their foliage during the winter or dry season.There are many different kinds of evergreen plants, both trees and shrubs...
tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
or large shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
growing to 20 m tall. The leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
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 flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s are produced 10-20 together in a racemose
Raceme
A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...
cyme
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
5-13 cm diameter; each flower is 15-18 mm diameter, yellowish green, without petals, but with a conspicuous ring of 40-70 stamen
Stamen
The stamen is the pollen producing reproductive organ of a flower...
s surrounding the 4-11 carpels. The fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
is 2 cm diameter, woody, star-shaped, composed of 4-11 follicles
Follicle (fruit)
In botany, a follicle is a dry unilocular many-seeded fruit formed from one carpel and dehiscing by the ventral suture in order to release seeds, such as in larkspur, magnolia, banksia, peony and milkweed....
, each follicle containing several seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s.
Trochodendron aralioides shares with Tetracentron the very unusual feature in angiosperms
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
, of lacking vessel element
Vessel element
A vessel element is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are typically found in the angiosperms but absent from most gymnosperms such as the conifers....
s in its wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
. 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
Angiosperm Phylogeny Group
The Angiosperm Phylogeny Group, or APG, refers to an informal international group of systematic botanists who came together to try to establish a consensus on the taxonomy of flowering plants that would reflect new knowledge about plant relationships discovered through phylogenetic studies., three...
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.