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The Genus Olearia
Ivan Holliday
Olearia belongs to the very large botanically complex daisy family Asteraceae that has the largest number of species of all flowering plant families in the world. In Australia most daisies are annuals, such as the many spectacular everlastings seen in masses after wet periods in the arid inland, or perennial herbs. However, a number of species of the Olearia genus are true shrubs with conventional daisy-like or ligulate flower heads. Olearias are found throughout Australia and also in New Zealand, usually displaying white, mauve, pink or purple flower heads.
What is an Olearia? The genus Olearia is distinguished by its tightly-packed composite heads with single-rowed ray florets enclosed by smalls- overlapping bracts, and its terete or slightly compressed achenes [fruits].
Olearia grandiflora is a low suckering, South Australian endemic, shrub found as an understory plant in semishade in eucalypt woodland or forest of the Mount Lofty Ranges near Adelaide. It is a many-stemmed, soft-wooded shrub to about 40 cm high but often spreading by underground root suckers. The leaves are dark shining green on the upper surface but white-tomentose beneath, mostly 4-10 cm long by 2-6 cm broad, on short petioles, ovate and denticulate, with prominent venation. The specific name refers to the large handsome flowers which form typical daisy-like heads, 6-7 cm across, with pure white ray florets, each ligule over 3 cm long, and yellow disc flowers in the centre. Each flower head is enclosed by an involucre of pubescent, acuminate bracts and is borne on a stout stalk 20-30 cm long. Flowering, November to December. The fruit is an achene about 2 cm long with many pappus bristles.
Olearia grandiflora has been a success having thrived for 30 years. It is growing in clay over limestone marl, receiving extra water in summer. It has spread underground, appearing nearby among other larger shrubs. Last summer, a long, dry, hot spell burnt the leaves badly but it has since recovered. It is best suited to well-drained but moist soil in semishade, producing numerous flower heads over several weeks.
Olearia pannosa, Silver Leaf Daisy, is a very similar shrub differing in its leaves, which are entire, and more often oblong or elliptic in shape, with tomentum extending to the upper surface. It grows in similar conditions in the Mount Lofty Ranges, where there is some intergrading between the two species, but is also widespread throughout South Australia and Victoria, extending to New South Wales.
Olearia pimeleoides is a widely distributed small shrub found in dry, sandy or gravelly soils extending from Western Australia to inland New South Wales. It is common in the northern parts of South Australia. It is a small, rounded, hoary, soft-wooded shrub, sometimes reaching 1 m high by about the same breadth, the leaves and branches covered with a soft woolly tomentum. The name refers to the shrub's superficial similarity to Pimelea. The leaves are oblong-cuneate to obovate, 4-12 mm long by 3-4 mm broad, white-tomentose below but usually glabrous on the upper surface, with recurved margins. Profuse, white, daisy-like flowers are produced in solitary terminal heads, 2.5 cm across, in spring. Bracts numerous, subacute and woolly toward tips. Fruit is a terete, silky- pubescent achene with 40-60 pappus bristles. This shrub prefers a well- drained, light soil in an open sunny situation and temperate conditions. I have seen it flourishing in footpath median strips in the limestone soils of Adelaide's northern suburbs. My only attempt in this clay soil, red/brown earth of the Adelaide plains, was a failure.
Olearia axillaris, Coast Daisy Bush. Good forms of this species are valued for their ornamental grey-white foliage. It is a shrub normally 1-2 m high with insignificant white flowers. An inhabitant of exposed coastal sand dunes throughout Australia such as those of Kangaroo Island, it is an excellent shrub for these conditions. Olearia axillaris is easy to grow in coastal sands and other well-drained sites.
Olearia ciliata. This small shrub under 30 cm high is found throughout many areas of Australia in sandy, or well-drained, light soils. The rough, tightly compacted, linear leaves, usually 10-15 mm long, have ciliate margins, and the flower heads on reddish stalks are purple or purplish blue with a yellow disc in the centre. The variety squamifolia is found only on Kangaroo Island, restricted to sandy laterite on the eastern half of the island. It has smaller, tightly compacted leaves. It is an attractive subject for the rock garden, flowering in spring.
Olearia microdisca, Small-flowered Daisy-bush, is found only on Kangaroo Island in heath and mallee and is endangered. An erect narrow shrub to 1-2 m high, it has sticky leaves and stems, flowering in autumn.
Olearia phlogopappa is grown frequently in Adelaide, particularly in the Mt. Lofty Ranges. All forms are very showy when in full flower, being covered with masses of pure white, pink or mauve flower heads, 1.5-2.5 cm across. It appears to require plenty of summer water.
Olearia rudis, Azure Daisy-bush, is a slender erect, few-stemmed shrub to 1 m high, the larger leaves more or less elliptic and evenly toothed. It grows in limestone mallee on Kangaroo Island and occurs in Western Australia, South Australia, Victoria, New South Wales and Queensland.
From Australian Plants, journal of the Association of Societies for Growing Australian Plants (ASGAP), December 2000.
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Australian Plants online - September 2004
Association of Societies for Growing Australian Plants
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