Tetradium is a genus of deciduous trees in the family Rutaceae (order Sapindales), native to temperate and tropical East Asia. The genus comprises around nine species distributed from India and Indo-China through China, Korea, and into the Malay Archipelago.
Trees in this genus are noted for their glossy pinnate leaves that resemble ash foliage, and for producing large flat corymbs of small white flowers in mid to late summer — typically July and August — at a time when few other trees of comparable size are in bloom. This late-season flowering makes Tetradium exceptionally attractive to bees, and the genus is highly valued by beekeepers as a source of late-summer honey. The flowers are followed by clusters of seed capsules that mature through autumn, starting as bright red and opening to expose shiny black seeds; these berries are readily consumed by birds.
The best-known member, Tetradium daniellii (the "bee-bee tree"), develops a smooth grey bark reminiscent of beech and can reach 20 metres in height. Its glossy dark-green leaves turn yellow-green in autumn before falling.
Tetradium is closely related to Melicope and is sometimes subsumed within it. In older literature, all species were placed in the genus Euodia (also spelled Evodia), but that name is now restricted to tropical members of the group; Tetradium covers the broader East Asian lineage. Plants in this genus serve as larval food plants for certain Lepidoptera, including Aenetus scotti and Endoclita damor.
Etymology
The genus name Tetradium relates to the Greek root tetra- (four), likely referring to the four-parted flowers characteristic of the genus. In older horticultural literature the plants appear as Euodia or Evodia (the Latin spelling variant), names still encountered in cultivation contexts.
Distribution
Tetradium occurs across temperate to tropical East Asia. Individual species range from India and Indo-China westward through southern and central China, north into Korea, and south into the Malay Archipelago. T. daniellii is native to China and Korea; T. ruticarpum spans India to northeast Asia; T. fraxinifolium is found from India through Indo-China into China.
Ecology
Tetradium flowers in late July and August, providing a significant late-summer nectar source when few other tree-sized plants are in bloom, making it highly attractive to bees and valued by beekeepers for honey production. The red-to-black seed capsules are eaten by birds. Caterpillars of the moths Aenetus scotti and Endoclita damor feed on Tetradium species.
Cultivation
Tetradium daniellii (bee-bee tree) is the most widely cultivated species in temperate gardens, grown for its ornamental smooth grey bark, attractive pinnate foliage, and abundant late-summer flower clusters that draw pollinators. It is adaptable to most well-drained soils and can reach 20 m; in temperate climates it is considered a low-maintenance, hardy specimen tree.
Taxonomy Notes
Tetradium was historically included within the genus Euodia (sometimes spelled Evodia). Current taxonomy restricts Euodia to tropical species and recognises Tetradium as the East Asian genus. The genus is also closely allied to Melicope, and some classifications subsume it there.
