Olearia is a large genus of shrubs and small trees in the family Asteraceae (the daisy family), commonly called daisy-bushes for the daisy-like composite flowerheads carried by every member of the group. In New Zealand the larger, tree-forming species are also known as tree daisies or tree asters. The genus belongs to subfamily Asteroideae, tribe Astereae, subtribe Brachyscominae, and was formally established by Conrad Moench in 1802 in the supplement to his Methodus. Olearia tomentosa is the type species, and the name honours Johann Gottfried Olearius, a 17th-century German scholar whose Specimen Florae Hallensis catalogued the plants around Halle.
Plants of the World Online currently accepts about 135 species, distributed across Australia, New Zealand and New Guinea, although GBIF lists 276 descendant taxa once synonyms and infraspecific names are counted. Roughly 130 species are endemic to Australia, where representatives occur in every state and territory, and 40 taxa are recognised in New Zealand — 37 of them indigenous endemics plus three casual exotic introductions. A 2020 taxonomic revision subsumed several formerly separate genera into Olearia, which is why the Australian Plant Census now treats the name as nomenclaturally conserved.
Members are evergreen shrubs or small trees, typically with alternate or opposite leaves that are densely tomentose (felted) on the underside, an adaptation shared by many species growing on exposed sites. The capitula are small to large, solitary or arranged in variously compound inflorescences, with a single row of ray florets surrounding a disc of bisexual disc florets. Ray colour ranges from pure white through pink and mauve to deep purple. Fruits are ribbed or striate achenes, usually pubescent to pilose, topped with a pappus of bristles that aids wind dispersal.
The genus occupies an unusually wide ecological range, from arid interior shrublands (Olearia arida, O. xerophila) to alpine herbfields (O. alpicola) and even wetland margins (O. hygrophila), which helps explain its diversity within a relatively compact geographic footprint. Several species — notably Olearia macrodonta (New Zealand holly), the hybrid O. × mollis, and O. × scilloniensis — are valued as garden ornamentals in temperate climates, where most are hardy to around −10 °C (14 °F) given a sheltered spot in full sun.
Etymology
The genus name Olearia commemorates Johann Gottfried Olearius, a 17th-century German scholar who authored Specimen Florae Hallensis, an early local flora of the region around Halle. Conrad Moench applied the name when he formally described the genus in 1802 in the supplement to his Methodus, designating Olearia tomentosa as the type species.
Distribution
Olearia is restricted to the Australasian region, with Plants of the World Online accepting about 135 species across Australia, New Zealand and New Guinea. Australia is the centre of diversity: roughly 130 species are endemic there, and ALA records confirm the genus is present in every Australian state and territory, including New South Wales, Victoria, South Australia, Western Australia, the Northern Territory and Tasmania. New Zealand holds 40 taxa — 37 indigenous endemics plus three casual exotic introductions — making Olearia one of the country's larger shrub-and-tree genera. GBIF lists 276 descendant taxa in total once synonyms and infraspecific names are included.
Ecology
The genus spans an unusually broad ecological range for an Asteraceae shrub group. Species are found in arid interior environments (Olearia arida, O. xerophila), in alpine and subalpine zones (O. alpicola), and in wetland or moisture-retaining habitats (O. hygrophila), reflecting strong adaptive radiation across Australasia's varied landscapes. The genus-wide habit — woody shrubs and small trees with tomentose leaf undersides — suits exposed, often windy or high-irradiance sites typical of coastal, montane and arid Australasian vegetation.
Cultivation
Several Olearia species are grown as ornamentals in temperate gardens, valued for their evergreen foliage and abundant daisy-like flowerheads in white, pink, mauve or purple. As a group they are generally hardy down to about −10 °C (14 °F), but require a sheltered position in full sun to perform well. The most widely cultivated taxa include Olearia macrodonta — known as New Zealand holly for its toothed, holly-like leaves — along with the garden hybrids Olearia × mollis and Olearia × scilloniensis.
Taxonomy notes
Olearia Moench (Asteraceae, tribe Astereae, subtribe Brachyscominae) was published in 1802 in Methodus Supplement, page 254, with Olearia tomentosa designated as the type species. The Australian Plant Census treats the name as nomenclaturally conserved (nom. cons.). A 2020 revision established multiple heterotypic synonyms, folding several formerly separate genera into Olearia and increasing its species count accordingly. GBIF currently records 276 descendant taxa under the accepted genus name.
Cultural uses
In New Zealand, some Olearia species carry Māori names that reflect long-standing cultural recognition, including akeake and heketara applied to particular tree daisies.
