Acacia saligna Seeds | Golden Wreath Wattle
LATIN NAME: Acacia saligna
COMMON NAME: Golden Wreath Wattle, Blue-Leaved Wattle
Plant Profile
Raise a golden wreath wattle and you get a plant with ferny true leaves. Give it time and the tree throws them away. Acacia saligna belongs to the group of wattles in which the leaf blade is abandoned altogether and the leaf stalk is promoted into its place: the flattened petiole, called a phyllode, carries the photosynthesis for the rest of the tree’s life. In the southwest of Western Australia, where this species is native and where the wattle genus dominates the flora, that single structural decision is one of the reasons wattles can hold a canopy through a summer with almost no rain.
The native habitat is coastal and near-coastal: deep siliceous sands, gravelly slopes and creek lines on the south-western edge of the continent, under a Mediterranean climate with wet winters and a hot summer that brings almost no rain. The tree is fast and fairly short-lived, and often multi-stemmed where it has been cut or burnt. It is easily confused with Australia’s floral emblem, the golden wattle, which has broader phyllodes and showier heads; the reliable separations are the narrow, often wavy phyllode margin and the shape of the flower clusters.
Planted for dune stabilisation, firewood and fodder, the species naturalised across the Mediterranean basin, Chile, California and southern Africa. In South Africa it is a declared invader, and its control became a landmark in biological control: a gall rust fungus, Uromycladium tepperianum, was introduced to attack the trees, and a seed-feeding weevil was added later to cut the soil seed bank. This is a rare case of a plant’s own pathogens being used to undo a planting decision.
Science & Biotechnology
Wound a stem and the tree bleeds a gum that is largely arabinogalactan, a branched polysaccharide with a protein component, related to the gum arabic of the Sahel acacias and investigated as a substitute for it in food and industrial use. The bark is the other chemical story: it is loaded with condensed tannins, the proanthocyanidins that made wattle bark a global tanning material. Both products came from the same tree, one from its surface and one from its trunk.
Uses & Benefits
As a legume, the species nodulates with slow-growing bradyrhizobia and fixes atmospheric nitrogen, which is why it was planted so widely outside Australia: in North African shelterbelts, in Middle Eastern fuelwood blocks, and on saline or sodic soils where little else will grow. Its tolerance of salt and of poor alkaline ground is the basis of its use in biosaline agroforestry. The trade-off is that the same toughness makes it a formidable coloniser, and the nitrogen it fixes changes the soil for everything growing around it.
Growing from Seed
The seedling starts bipinnate, with a rachis and leaflets, exactly as you would expect from a legume. Transitional foliage follows, and then the mature shoots carry phyllodes only. Botanists read the phyllode as a petiole that has become flattened and dorsiventral, with stomata on both faces and a rim of thickened tissue at the margin.
Hold one up and the anatomy is plain: a single raised midrib runs its whole length, the surface is waxy and blue-green, and there is a small gland near the base where the phyllode joins the stem. There is no blade, no rachis and no leaflets, only a stalk doing a leaf’s work. Phyllodes of this species are held at a steep angle, so the harsh midday sun tends to strike them near edge-on. The flowers follow as golden globular heads in short axillary racemes in late winter and spring, and the pods are narrow and flat, pinched between the seeds.
The seed coat is hard and waxy, and water cannot get through it, so treat the seed before sowing. Pour just-off-the-boil water over the seed and let it stand until cool, or nick the coat with a file opposite the small pale aril. Sow one centimetre deep in a free-draining mix, two seeds to a small pot, and keep the medium moist but never soggy. Move the seedlings on as soon as the first phyllodes have replaced the bipinnate juvenile leaves, which is the signal that the root system is ready to travel.
Our Take
Golden wreath wattle is a fast, generous plant for a dry, exposed site, and it earns its place where you need a windbreak or cut foliage within a couple of seasons. Grow it as a coppiced shrub rather than a specimen tree and you get the best of it. If you are collecting wattles, black wattle shares the tannin-bark history, silver wattle belongs to the cut-flower trade, and the willow-leaf wattle is the more restrained garden alternative. For nitrogen-fixing fodder and coppice on poor ground, compare Leucaena.
Related Reading
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