Acacia macradenia Benth.

Stem Characteristics

Acacia macradenia Benth. has hairless, smooth branches. Generally, younger stem sections are green, while older stem sections are brown.

Phyllode Structure

Its leaf-like structures, called phyllodes, are actually flattened petioles (leaf stalks); true leaves are initially bipinnate. Older phyllodes are darker, longer, and lanceolate in shape, while younger phyllodes are much smaller.

Size and Growth Form

This plant or tree can grow up to 5 meters tall, with a spread of up to 4 meters. Its branches are pendulous (loosely hanging) to subpendulous and flexuose (readily bending).

Flower Cluster Morphology

Small, yellow, globular flower clusters grow at stem stalks. Each cluster holds between 35 and 50 individual flowers; each flower has five petals, five sepals, and many stamens, which give full-bloomed clusters a soft appearance.

Flowering Period

Flower cluster development depends on weather, with optimal flowering occurring at temperatures from February through March.

Flower and Phyllode Growth Pattern

Developing flower clusters show visible red areas when they start growing; if no flower clusters form, existing phyllodes continue to grow in an alternating pattern.

Fruit Characteristics

The fruits are black pods, which give the species its common name zig-zag wattle. These pods are small, curved, have a smooth outer casing, and have a structure similar to a lima bean.

Pod Maturation

Pods start out green, then turn brown-black as temperatures rise through spring, until they reach full maturation. Fully mature pods can grow up to 12 centimeters long.

Seed Morphology

Inside the pods are hard, brown, bean-shaped seeds.

Germination Temperature Response

One experiment testing how temperature affects Acacia macradenia seed germination found that seeds treated with hot water had higher germination rates than seeds treated with cooler water.

Native Distribution

This species is native to Australia, where it occurs naturally across Central Queensland, and is cultivated in regions around Chinchilla and Pentland.

Non-Native Range

Due to its invasive growth habit, it has also been recorded growing outside its native range in places such as Ipswich parks.

Natural Habitat

Acacia macradenia is a shrub that grows best in cool to warm climates, in sandy or gravelly areas near creeks.

Cold Temperature Effects

Cold temperatures prepare seeds and enhance stronger flowering when temperatures rise again.

Air Pollution Tolerance

Experiments testing tolerance have found this species can adapt to air-polluted areas: seeds grown in environments with different concentrations of air pollution maintained stable photosynthetic and transpiration rates, similar to rates seen in non-polluted environments.

Cultivation Requirements

For cultivation, Acacia macradenia prefers a well-drained position and full sun. It has been successfully cultivated in coastal areas of eastern Australia, from Townsville south to Melbourne.

Frost Sensitivity

However, plants have died from heavy frosts in some inland locations, including Canberra.