Golden Wattle (not native)

“Pride is like the beautiful acacia, that lifts its head proudly above its neighbor plants- forgetting that it too, like them, has its roots in the dirt.” Christian Nestell Bovee. (Intuitions and Summaries of Thought, 1862)

Species of Acacia, many with billowing masses of fragrant, yellow flowers, are among our best known California landscape plants. But many are also on the state Invasive Species list – plants that have escaped from the landscape into wildlands, where they replace native species and disrupt community relationships.

Golden wattle (Acacia pycnantha) is native to southeastern Australia and was named the national flower of Australia in 1988. Decades ago, many were planted in San Elijo Ecological Reserve to shelter and obscure a hunting lodge that once nestled against the hills on the south side. They may have been planted as understory for the sugar gums (Eucalyptus cladocalyx) still growing there. The golden wattles have made themselves at home and decades later, for better or worse, are still decorating the entrance to Annie’s Canyon in late-winter yellow.

Description ^2,235,475

Golden wattle is a variable large shrub or small tree, erect or spreading to 26 feet (8 m) high. The bark is green on young branches, turning gray or brown when older, smooth or with fine furrows. True leaves are absent. What appear to be leaves are flattened petioles (technically called phyllodes; Plant Guide will continue to use the term “leaf”). Leathery leaves are one to eight inches (2-20 cm) long, elliptic or oblanceolate with acute tips and smooth margins. They are often somewhat sickle-shaped, resembling some eucalyptus leaves. Some leaves have one or two small swollen areas, nectar glands, on the margin near the base. Occasionally, a small seedling will have a few true leaves; these are compound, twice-divided pinnately and delicate in appearance; they persist for only a short time.

Tiny, bright yellow flowers are crowded into spherical flower heads which, in turn, are arranged into showy elongated clusters from leaf axils. At the base of each tiny flower is a tiny, scale-like bract, more apparent in the bud stage. Tan, papery, fringed sepals and yellow petals are inconspicuous. Numerous yellow stamens are exerted beyond the petals on crooked filaments surrounding a single pistil. A slim style with a minute stigma can sometimes be seen extending beyond the stamens. Golden wattle blooms in late winter and early spring (July – November in Australia,²³⁵ Feb-April in our area.⁷)

The fruit of golden wattle is the typical legume of the pea family – a narrow and elongated pod five or six inches (14 cm) long, straight or slightly twisted, flattened and constricted between seeds. Seeds are attached along one side of the pod. On maturity, pods split along the side opposite the seeds. The dark seeds are about 1/2 inch (0.6 cm) long, oval and somewhat shiny. A fleshy, club-shaped structure (elaiosome or aril) is attached at one end.^476,477

Classification ^{2,44,143,475,476}

Golden wattle is a dicot angiosperm in the pea family (Fabaceae, formerly Leguminosae), the third largest family of flowering plants. Acacia belongs to the Mimosoideae, a subfamily that lacks the distinctive bilateral (papilionaceous) flowers of most peas and is characterized instead by inconspicuous petals and numerous long, exerted stamens, often crowded into catkins or spheres. Leaves in the pea family are often compound. The fruit is a one-chambered pod that splits open on maturity; the seeds are anchored along one side. Many members of the pea family, including golden wattle, harbor nitrogen-fixing bacteria in special root nodules, allowing them to convert and use atmospheric nitrogen from the air.⁴¹

The Acacia genus is large and diverse, with over 1000 species.^{475, 478} The Australian acacia are typically called “wattles.” Many botanists believe that the present genus should be divided into several genera but there is little agreement about the details. Currently, golden wattle has no recognized subspecies.

Twenty-seven members of the pea family have been reported in the Reserve,⁴⁸ many of them non-native species including seven species of Acacia. Common native peas include deerweed (Acmispon glaber), ocean locoweed (Astragalus trichopodus) and collared lupine (Lupinus truncatus).

Ecology ^41,479

Many plants include nectar in their arsenal of pollinator-attractants. In most cases, the nectar glands are closely associated with the flower, often deep within the flower’s throat. In most acacias, however, the nectar glands are not in or on the flower, but on the nearby leaves. In golden wattles, for instance, many leaves (but not all) have one or two small nectar glands on the leaf margin, near the leaf base. These are small swellings topped by a shallow depression; they resemble small galls.

Studies in Australia show that golden wattle is at least partially pollinated by birds, especially Honeyeaters, Silvereyes, and Thornbills. These are attracted to the nectar (or to insects attracted by the nectar) and brush their heads against the flowers while removing nectar from the nearby leaves. A contrasting theory suggests that the nectar glands attract ants, which in turn guard against Roselles, birds which prey on the flowers to the detriment of the acacia. However, we have neither Honeyeaters, Roselles or guard ants in the Reserve, so the pollination pathways of our trees may be quite different. One can easily watch bees gather pollen from the flower heads; perhaps bees are the main pollinators here.

In spite of the fact that the flower head resembles many wind-pollinated tree catkins, acacia pollen grains are too large and too heavy to be wind-carried,⁴⁸⁰ and wind does not appear to be an important pollinator.

Human Uses

Aborigines had many uses for parts of acacias, including food, binding and weaving material, spear shafts and ax handles, boomerangs and firewood. Acacia gum was chewed or used for adhesive.⁴⁷⁶

Today, acacia species are best known in California as landscaping and garden plants. Unexpectedly, golden wattle is not one of the more commonly planted.²¹⁴

Some species of acacia (especially A. senegal, native to parts of Africa and India) are the source for gum arabic, a substance commonly used as a binding agent in everything from jelly beans to wine, art, shoe polish and pyrotechnics.⁴¹

Golden wattle appears most frequently used for its bark which is especially rich in tannin and for which these trees are commercially harvested.⁴¹

Interesting Facts ^41,475

In 1988, the occasion of Australia’s bicentennial celebration, golden wattle was made the national flower of Australia, and September 1 was declared Wattle Day. This species has been featured on several Australian postal stamps.