| Trochodendraceae | |
|---|---|
 | |
| Trochodendron aralioides | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Trochodendrales Takhtajan exCronquist |
| Family: | Trochodendraceae Eichler |
| Genera | |
Trochodendraceae is the onlyfamily offlowering plants in the orderTrochodendrales. It comprises two extantgenera, each with a singlespecies[1] along with up to five additional extinct genera and a number of extinct species.[2] The living species are native to south east Asia. The two living species (Tetracentron sinense andTrochodendron aralioides) both have secondary xylem withoutvessel elements, which is quite rare in angiosperms. As the vessel-free wood suggests primitiveness, these two species have attracted much taxonomic attention.
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Tetracentron andTrochodendron are deciduous or evergreentrees, which grow to between 20–30 m (66–98 ft) tall, withTrochodendron sometimes sporting umbrella-shaped branches.
Pollination is probably myriophyllous, even thoughTetracentron shows a clear anemophilous syndrome. The pulverulent seeds are dispersed by the wind (anemochory).Trochodendron is present in both protandrous and protogynous forms that are self-compatible.
The plants are found in wooded formations,Trochodendron between 300 m and 2.700 m above sea level andTetracentron between 1.100 m and 3.600 m above sea level.
Flavonoids (quercetin and kaempferol) andproanthocyanidins (cyanidin anddelphinidin) are present.Epicuticular waxes are basically composed of nonacosan-10-ol.[citation needed]Tetracentron containschalcones ordihydrochalcones.Trochodendron containsmyricetin.Ellagic acid is absent.
Trochodendron and the fossil genusEotrochion are known from thePaleocene of Wyoming, which constitute the oldest records of the family.[2]
A diverse assemblage of trochodendraceous species have been described from theEocene Okanagan Highlands in British Columbia and Northeastern Washington. The monotypic generaParaconcavistylon andPentacentron are accompanied byTetracentron hopkinsii and theTrochodendroninfructescence morphospeciesTr. drachukii plus the foliage morphospeciesTr. nastae.[3][2]
The fruit and wood genusNordenskioeldia, along with the associated leaf morphogenusZizyphoides have been considered part of Trochodendraceae, though phylogenetic analysis by Manchesteret al (2020) suggested they might be better placed as a basal stem lineage in the Trochodendrales, rather than as a crown group member of the family Trochodendraceae.[2]
The Trocodendraceae are a group of flowering plants that include the cladeEudicotyledoneae. In previous systems they have been related with theCercidiphyllaceae and theEupteleaceae, with which they share some characteristics that can be considered symplesiomorphic or convergent and that have been excluded from the order Trochodendrales because of molecular data leaving the Trocodendraceae isolated. Based on molecular and morphological data, the APW (Angiosperm Phylogeny Website) considers that it constitutes the only family in the Order Trochodendrales (cf.AP-website).
The current classification of Trochodendraceae is theAPG IV system published in 2016, which maintains the circumscription of Trochodendraceae used in theAPG III system published in October 2009. Unlike theAPG andAPG II systems, the later systems place the family as the only family in the order Trochodendrales. They also includesTetracentron, synonymizing Tetracentraceae fully with Trochodenraceae.[4][5]
TheAPG II system, of 2003 retained the classification used in the 1998APG system recognizing Trochodendraceae as a family. APG and APG II did not place the family in anorder, leaving it among the basal lineages of theeudicots. Both APG systems accepts this as a family of two modern species, but it does allow the option of separating out the familyTetracentraceae.
This segregation would lead to two families with one species each: Tetracentraceae withTetracentron sinense and Trochodendraceae withTrochodendron aralioides.
TheCronquist system, of 1981, accepted both Trochodendraceae and Tetracentraceae as families and placed these in the order Trochodendrales, in subclassHamamelidae, in classMagnoliopsida.
The family includes two living genera with very different morphological characteristics:
{{cite web}}: CS1 maint: multiple names: authors list (link)
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