Olearia, most commonly known as daisy-bush, is a genus of flowering plants belonging to the family Asteraceae, the largest of the flowering plant families in the world. Olearia are found in Australia, New Guinea and New Zealand. The genus includes herbaceous plants, shrubs and small trees. The latter are unusual among the Asteraceae and are called tree daisies in New Zealand. All bear the familiar daisy-like composite flowerheads in white, pink, mauve or purple.

Description

Plants in the genus Olearia are shrubs of varying sizes, characterised by a composite flower head arrangement with single-row ray florets enclosed by small overlapping bracts arranged in rows. The flower petals are more or less equal in length. The centre of the bi-sexual floret is disc shaped and may be white, yellowish or purplish, generally with 5 lobes. Flower heads may be single or clusters in leaf axils or at the apex of branchlets. Leaves may be smooth, glandular or with a sticky secretion. The leaves may grow opposite, alternate, arranged sparsely or clustered. Leaf margins either entire or lobed, with or without a stalk. The fruit are dry slightly compressed, one-seeded, narrow-elliptic or egg-shaped with longitudinal ridges and smooth or with sparse hairs.

Taxonomy and naming

The genus Olearia was first described in 1802 by Conrad Moench in Supplementum ad Methodum Plantas and is named after Johann Gottfried Olearius, a 17th-century German scholar and author of Specimen Florae Hallensis. Originally a large genus, a molecular study has found it to be polyphyletic.

Distribution

There are approximately 180 species of Olearia, of which about 112 species are endemic to Australia. Olearia are found in all states of Australia.

Species

The following is a list of Olearia species accepted by the Australian Plant Census or the New Zealand Plant Conservation Network or listed in the Census of Vascular Plants of Papua New Guinea as at May 2021:

Use in horticulture

Several species are cultivated as ornamental garden plants, and there are hybrids of uncertain or mixed parentage. Among these, the following have been given the Royal Horticultural Society's Award of Garden Merit:- They are generally hardy down to -10 C, but require a sheltered spot in full sun.