A peculiarity largely developed in the mimosa family is the tendency for the true leaves to be suppressed, and their place taken by the flattened and expanded midrib (phyllode). Thus leaves of two very distinct forms are common in the genus, and some acacias, as A. heterophylla, may have both forms on the same branch. Compare A. pycnantha and A. decurrens.
The Australian mimosas have been naturalised in India, and grow freely in the Nilgiri Hills, but the bark does not appear to be utilised.
The most important species are as follows:—
A. pycnantha. ([Fig. 61].) “Broad-leaved” or “Golden Wattle,” South Australia. One of the strongest tanning barks known. A sample marked “special,” analysed in the Yorkshire College, contained 50 per cent. of tannin; another sample marked “ordinary” contained 40 per cent.
Fig. 61.—Broad-leaved Wattle (Acacia pycnantha).
Fig. 62.—Green Wattle (Acacia decurrens).
A. longifolia, the Golden Wattle of New South Wales, only contains half as much tannin as A. pycnantha.
A. mollissima, with its two varieties A. decurrens ([Fig. 62]) and A. dealbata, are among the most important of the Wattle family commercially. Two samples of the former marked “Green Wattle” showed 36-39 per cent. of tanning matter; another sample marked “Sydney Green Wattle,” contained 41 per cent. A sample of A. decurrens, the second variety, was much weaker, showing only 12 per cent. on analysis.