''Trochodendron'' is a genus of

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

s with one living species, ''

Trochodendron aralioides ''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 ...

'', and six extinct species known from the fossil record. It was often considered the sole genus in the family Trochodendraceae, though botanists now also include the distinct genus '' Tetracentron'' in the family.

Species

* ''

'' *†'' Trochodendron beckii'' *†'' Trochodendron drachukii'' (Infructescence; Ypresian,

McAbee Fossil Beds The McAbee Fossil Beds is a Heritage Site that protects an Eocene Epoch fossil locality east of Cache Creek, British Columbia, Canada, just north of and visible from Provincial Highway 97 / the Trans-Canada Highway ( Highway 1). The McAbee ...

, British Columbia) *†'' Trochodendron evenense'' (Leaves; Miocene, Kamchatka) *†'' Trochodendron infernense'' (Infructescence; Late Palaeocene,

Fort Union Formation The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. In the Powder River Basin, it contains important economic deposits of coal, uranium, and coalbed methane. ...

) *†'' Trochodendron kamtschaticum'' (Infructescence; Miocene, Kamchatka) *†'' Trochodendron nastae'' (Leaves; Ypresian,

Klondike Mountain Formation The Klondike Mountain Formation is an Early Eocene (Ypresian) geological formation located in the northeast central area of Washington (state), Washington state. The formation is composed of volcanic rocks in the upper unit and volcanic plus lacu ...

, Washington state) *†'' Trochodendron postnastae'' (Leaves; Langhian, Moose Mountain Flora, Oregon) *†'' Trochodendron protoaralioides'' (Leaves; late Miocene, Japan) *†'' Trochodendron rosayi'' (Infructescence; Langhian, Moose Mountain Flora, Oregon) ''Trochodendron'' is native to

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

, southern

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

and the

Ryukyu Islands The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Geography of Taiwan, Taiwan: the Ryukyu Islands are divided into the Satsunan Islands (Ōsumi Islands, Ōsumi, Tokara Islands, Tokara and A ...

, with fossils known from

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, and the Russian Far East. ''Trochodendron aralioides'' is an

evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional throughout the year. This contrasts with deciduous plants, which lose their foliage completely during the winter or dry season. Consisting of many diffe ...

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

or large

shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...

growing to 20 m tall. ''Trochodendron'' and ''Tetracentron'' lack

vessel element A vessel element or vessel member (also called a xylem vessel) is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are found in most angiosperms (flowering plants) and in some gymnosperms such as cyca ...

s in their

wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

, a quite unusual feature in

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit. T ...

. 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 The Angiosperm Phylogeny Group (APG) is an informal international group of systematic botanists who collaborate to establish a consensus on the taxonomy of flowering plants (angiosperms) that reflects new knowledge about plant relationships disc ...

has shown it to be in a less basal position (early in the

eudicot The eudicots or eudicotyledons are flowering plants that have two seed leaves (cotyledons) upon germination. The term derives from ''dicotyledon'' (etymologically, ''eu'' = true; ''di'' = two; ''cotyledon'' = seed leaf). Historically, authors h ...

s), suggesting the absence of vessel elements in these two genera is a secondarily evolved character, not a primitive one.

Fossil record

Among the middle

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

Sarmatian The Sarmatians (; ; Latin: ) were a large confederation of Ancient Iranian peoples, ancient Iranian Eurasian nomads, equestrian nomadic peoples who dominated the Pontic–Caspian steppe, Pontic steppe from about the 5th century BCE to the 4t ...

palynoflora from the

Lavanttal The Lavanttal ('Lavant Valley', , Gams, Ivan. 1992. "Labotska dolina." ''Enciklopedija Slovenije'', vol. 6. Ljubljana: Mladinska knjiga, pp. 87–87. or ; Southern Bavarian: ''Lovnthol'') lies in the Lavanttal Alps in southern Austria in the eas ...

Basin

Austria Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...

researchers have recognized ''Trochodendron''

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

pollen Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...

. The sediment containing the ''Trochodendron'' fossil pollen had accumulated in a lowland wetland environment with various vegetation units of mixed evergreen/deciduous broadleaved/conifer forests surrounding the wetland basin. Key relatives of the fossil taxa found with ''Trochodendron'' pollen are presently confined to humid warm temperate environments, suggesting a

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones immediately to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Ge ...

climate during the middle Miocene in Austria.

References

External links

Flora of China: ''Trochodendron''

i
L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants.
{{Taxonbar, from=Q1857662 Eudicot genera Trochodendrales