A very large genus of trees and shrubs found in many tropical and warm temperate regions, but more especially in Australia and Africa. In Australia the acacias and eucalyptuses are the dominant genera of woody plants, and of the former there are now about 400 species recognised. The best known of them in this country is A. dealbata, the ‘silver wattle’, sprays of which are imported as ‘mimosa’ in winter from the south of France in great quantities to the London flower market.
The leaves of acacias are normally doubly pinnate, but in a large number of species this type of leaf disappears after the seedling stage and becomes reduced to a mere development of the leaf-stalk – what is known as a ‘phyllode’. These phyllodes are of one piece, flat and leaf-like, often of considerable size, and perform the same functions as ordinary leaves.
The flowers of all cultivated acacias are of some shade of yellow, varying from bright to very pale, and they are borne either in ball-like clusters or in cylindrical ones like tiny bottle-brushes. The stamens constitute the most conspicuous feature of the blossom, which is very different in structure from the typical pea-like flower of the family.
The species selected for the descriptive notes that follow are the most important of those that are, or have been grown in the milder parts of the British Isles. They include the majority of those most valued by Australian gardeners and are a good representation of the genus as a whole. None is so hardy as to be quite exempt from the risk of severe damage or death in hard winters, but A. dealbata, the best-known and most widely grown of the acacias, comes through most winters in the south of England with wall protection and is common as an open-ground plant in S. Cornwall; many others might be tried on a sunny, sheltered wall, where, thanks to their rapid growth, they may give many seasons of flower before the next killing winter supervenes. It should be added that many of the species have a wide natural range and might yet yield hardier forms than those now in cultivation.
The acacias are easily raised from seed but selected forms must be increased by cuttings of half-ripened wood and struck with gentle bottom heat. They will grow in any good garden soil provided it is not excessively limy; A. longifolia and A. rhetinodes are known to be exceptionally lime-tolerant.