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A genus of over 100 species of evergreen shrubs or small trees, confined to the Australasian region. Leaves alternate or opposite, usually tomentose beneath. Flower-heads resembling those of Aster, with yellow, white, or purplish disk-florets and white, purplish, or bluish ray-florets. The bracts of the involucre are imbricate in several series, and by this character Olearia can be distinguished from Senecio, some shrubby species of which superficially resemble some olearias in habit; in Senecio the bracts are in one row (apart from sometimes a few smaller outer ones).
There is no monographic treatment of the genus. Unpublished studies by Caroline Haycock show that the species fall into three distinct series of which probably only the first should properly be referred to the genus Olearia. This comprises all the species with T-shaped, stellate, or peltate leaf-hairs, and includes the majority of the cultivated species. The second series is Australian and includes here only O. ramulosa and the species dealt with under it. The third series is made up of the large-headed New Zealand species O. chathamica, O. colensoi, O. semidentata, and their allies. These are but distantly related to the true olearias, and perhaps would better be referred to the genus Pleurophyllum. If they are to be retained in Olearia, it is illogical to recognise the genus Pachystegia, which differs from the true olearias in comparatively minor characters. The species concerned is accordingly restored to Olearia in the present work (see O. insignis).
The late Lord Talbot de Malahide in Journ. R.H.S., Vol. 90, pp. 207-17 and 245-50 (1965), discusses the relative hardiness of the cultivated species and hybrids, and confirms that O. × haastii alone is generally hardy. Nevertheless, over sixty species and hybrids have been in cultivation outdoors in the British Isles and of these about twenty-five are hardy enough to survive the average winter in all but the coldest parts. The olearias are particularly useful for shelter in the maritime areas of the west and south-west, being resistant to sea winds (see W. Arnold-Forster, Shrubs for the Milder Counties, pp. 22-3 and Chapter XII). Horticulturally the majority are undemanding. A light loamy or peaty soil suits most of them. Almost all root quite readily from cuttings made of moderately ripened wood and placed in a cold frame.
The following works will be found useful for identification of olearias: H. H. Allan, Flora of New Zealand, Vol. 1, pp. 657-74 (1961); A. L. Poole and N. M. Adams, Trees and Shrubs of New Zealand, pp. 186-97 (1963); N. C. W. Beadle, O. D. Evans and R. C. Carolin, Flora of the Sydney Region, pp. 454-5 (1972); W. M. Curtis, The Student's Flora of Tasmania, Vol. 2, pp. 300-9 (1963); and J. H. Willis, AHandbook to Plants in Victoria, Vol. 2, pp. 685-98 (1972).
Revised by C. Jeffrey of the Herbarium, Royal Botanic Gardens, Kew.