Tristania is a monotypic

Monotypic

In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...

 genus, native to New South Wales

New South Wales

New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...

, Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, closely related to Cistemon

Bottlebrush

Callistemon is a genus of 34 species of shrubs in the family Myrtaceae, all of which are endemic to Australia. It is sometimes considered a synonym of Melaleuca, and four Callistemon species from New Caledonia were moved to that genus by Lyndley Craven and John Dawson in 1998...

. The genus had a number of species, but some have been reclassified as Lophostemon

Lophostemon

Lophostemon is a genus of 4 species of evergreen tree in the myrtle family Myrtaceae. All four species are native to Australia, with one extending to New Guinea. The genus is a relatively recent creation; all 4 species were previously included in the related genus Tristania.The most well-known...

and Tristaniopsis

Tristaniopsis

Tristaniopsis is a genus of 40 species of shrub and tree in the myrtle family Myrtaceae. They have a wide distribution, ranging from Burma, Thailand, Malesia, New Caledonia and Australia.Species include:*Tristaniopsis lucida...

.

The sole species in the genus is T. neriifolia.

It is a small 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...

, with dense branching. 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 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...

, opposite, simple, lanceolate, from 5–9 cm long and 1 cm broad. 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 in dense clusters of 3-15 together; each flower is 1-1.5 cm diameter, with five small yellow petals and numerous conspicuous stamens.

It is commonly known as the water gum.