Acacia, commonly known as wattles or acacias, is a genus of about 1,084 species of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. It was described by the Swedish botanist Carl Linnaeus in 1773 based on the African species Acacia nilotica. They are primarily found in Africa, Australia, and parts of Asia, but also in the Americas due to introduction.
Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not. All species are pod-bearing, with sap and leaves often bearing large amounts of tannins and condensed tannins that historically found use as pharmaceuticals and preservatives. Acacias often have unique features like bipinnate leaves, small leaves or phyllodes (flattened leaf stems), and many species have thorns or spines. Their flowers are small, white or yellow, and very fragrant, appearing in clusters (inflorescences).
Many acacia species have a symbiotic relationship with nitrogen-fixing bacteria in their root nodules, allowing them to convert atmospheric nitrogen into a form usable by plants, thus enriching the soil. Some Acacia species have become invasive outside their native ranges, particularly in Australia where they can alter ecosystems by changing soil nitrogen levels and outcompeting native flora.
Types of Acacia
Acacia melanoxylon (Blackwood, Australian Blackwood)
- Characteristics: This tree grows up to 30 meters tall with dark bark. Its wood is highly valued for its beauty and strength. Leaves are bipinnate, but phyllodes (flattened petioles) replace them in maturity. Flowers are yellow, and the tree produces elongated pods.
- Distribution: Native to southeastern Australia, it has been introduced to other parts of the world, including South Africa, New Zealand, and parts of Europe.
Acacia dealbata (Silver Wattle, Mimosa)
- Characteristics: Known for its silvery, feathery foliage and bright yellow, fragrant flowers, this tree can reach 10 meters in height. It’s noted for its fast growth and is often used for ornamental purposes.
- Distribution: Native to southeastern Australia, widespread in cultivation in temperate zones around the world.
Acacia nilotica (Gum Arabic Tree)
- Characteristics: Thorny tree up to 20 meters tall, with a wide-spreading crown. It produces gum arabic, a substance used in various industries. The tree has bright yellow flowers and pods that are often eaten by wildlife.
- Distribution: Found across Africa, the Arabian Peninsula, and into India. Commonly found in savanna regions.
Acacia koa (Koa)
- Characteristics: A large tree, often growing to 20 meters, known for its beautiful, dark, red-brown wood used in furniture and musical instruments. The leaves are bipinnate, and flowers are yellow.
- Distribution: Endemic to the Hawaiian Islands, mainly on the islands of Hawaii, Maui, and Kauai.
Acacia pycnantha (Golden Wattle)
- Characteristics: Australia’s floral emblem, this species has phyllodes rather than leaves, bright yellow flowers in clusters, and grows up to 8 meters tall. It’s drought-resistant and can fix nitrogen in the soil.
- Distribution: Predominantly in southeastern Australia, especially in Victoria and South Australia.
Acacia saligna (Coastal Wattle, Orange Wattle)
- Characteristics: Grows up to 6 meters, with long, narrow phyllodes resembling willow leaves. Produces masses of yellow flowers which cover the tree, making it very ornamental.
- Distribution: Native to Western Australia, but widely planted elsewhere for dune stabilization and as an ornamental.
Acacia tortilis (Umbrella Thorn Acacia)
- Characteristics: Recognizable by its flat-topped canopy, this tree has a broad trunk and twisted branches with long, curved thorns. The pods are often spiraled.
- Distribution: Widespread across Africa, from the Sahara to South Africa, and into the Middle East.
Acacia mangium (Mangium, Black Wattle)
- Characteristics: Fast-growing, reaching 30 meters, with a straight trunk. Used in forestry for timber and pulpwood. Leaves are bipinnate, and it has creamy-white to pale yellow flower heads.
- Distribution: Originally from Papua New Guinea and Queensland, Australia, now widely planted in Southeast Asia and South America for plantation forestry.
Acacia auriculiformis (Ear-pod Wattle, Northern Black Wattle)
- Characteristics: Medium-sized tree with sickle-shaped phyllodes and distinctive curved pods. It’s used for erosion control, fuelwood, and timber.
- Distribution: Native to northern Australia, Papua New Guinea, and Indonesia; extensively planted in tropical regions for afforestation.
Acacia longifolia (Sydney Golden Wattle, Sallow Wattle)
- Characteristics: Known for its long, narrow phyllodes, this species can grow up to 10 meters. Its flowers are bright yellow and very showy, making it a popular ornamental plant.
- Distribution: Native to southeastern Australia, but introduced as an ornamental in many countries where it can become invasive.
Acacia catechu (Khair, Cutch Tree)
- Characteristics: A small to medium-sized tree, known for its durable heartwood used in tanning, dyeing, and in traditional medicine. It has bipinnate leaves, yellow flowers, and produces pods.
- Distribution: Found in the Indian subcontinent, and extending into Southeast Asia.
Acacia sieberiana (Paperbark Thorn)
- Characteristics: Named for its peeling bark, this tree can grow up to 15 meters. It has long, straight thorns and yellow flowers. The wood is used for fuel and construction.
- Distribution: Widespread across Africa, from Ethiopia to South Africa.
Acacia farnesiana (Sweet Acacia, Huisache)
- Characteristics: A shrub or small tree with spherical yellow flowers that are very fragrant, used in perfumery. The tree has spines and produces pods containing seeds.
- Distribution: Originally from the Americas, it has been introduced to many tropical and subtropical regions worldwide.
Acacia erioloba (Camel Thorn)
- Characteristics: A tree with a wide, spreading crown, often seen in arid areas. It has a hard, durable wood, and its seeds are an important food for wildlife. It’s named for the thorns which protect its foliage.
- Distribution: Predominantly in the Kalahari Desert and surrounding areas, from South Africa to Botswana and Namibia.
Acacia senegal (Senegal Gum Acacia, Gum Arabic Tree)
- Characteristics: One of the main sources of gum arabic, this tree has a thorny trunk and branches, with flowers ranging from cream to pale yellow. The gum is harvested from the bark.
- Distribution: Native to the Sahel region of Africa, stretching from Senegal to Sudan.
Acacia mearnsii (Black Wattle)
- Characteristics: Fast-growing and often considered invasive, this tree is used for tanning due to the tannin in its bark. It has dark green, feathery leaves and produces clusters of cream-colored flowers.
- Distribution: Originally from southeastern Australia, widely spread in South Africa, India, and other regions.
Acacia decurrens (Green Wattle, Early Black Wattle)
- Characteristics: Known for its early flowering, with bright yellow, fluffy blooms. It’s used in tanning and dyeing. The tree can form thickets and is considered invasive in some areas.
- Distribution: Native to eastern Australia, naturalized in other parts of the world.
Acacia xanthophloea (Fever Tree)
- Characteristics: Known for its yellow bark, which was historically associated with fever (though not the cause of it). It has a rounded crown, bipinnate leaves, and yellow flowers.
- Distribution: Grows in East Africa, particularly in swampy areas.
Acacia karroo (Sweet Thorn, Karee)
- Characteristics: A small to medium-sized tree with a wide-spreading crown, used for fodder, fuel, and timber. It has long thorns, bipinnate leaves, and yellow flowers.
- Distribution: Widely distributed in South Africa, extending into southern Africa.
Acacia polyacantha (White Thorn Acacia)
- Characteristics: Can grow quite large with a thorny trunk and branches. It’s drought-resistant with white to cream-colored flowers. The wood is used for construction, and the tree provides browse for animals.
- Distribution: Found across East Africa, from Ethiopia through to South Africa.
Acacia aneura (Mulga)
- Characteristics: Often considered the quintessential tree of the Australian outback, Mulga is an evergreen shrub or small tree that can grow up to 8 meters. It’s highly drought-resistant with a deep root system, grey-green leaves, and small, yellow flowers. Mulga wood has been traditionally used by Indigenous Australians for various purposes, including weapons and musical instruments.
- Distribution: Predominantly found in the arid regions of Australia, especially in the Great Victoria Desert and the Western Plateau.
Acacia seyal (Red Acacia)
- Characteristics: This tree is notable for its role in ancient Egyptian culture, where it was used as incense. It has a distinctive red gum which exudes from wounds in its bark. The tree grows up to 17 meters tall, with thorny branches, small bipinnate leaves, and produces yellow flower spikes.
- Distribution: Native to the Middle East and North East Africa, particularly widespread in Sudan, Ethiopia, and parts of the Arabian Peninsula.
Acacia hockii (Mudzi tree)
- Characteristics: A species with a distinctive umbrella-shaped crown, commonly found in woodland savannahs. It features long, sharp spines, compound leaves, and small, cream-colored flowers. Its pods are flat and somewhat curved, providing food for wildlife.
- Distribution: Primarily in East and Central Africa, including countries like Kenya, Tanzania, Uganda, and Zambia.
Acacia coriacea (Wirewood, Dogwood)
- Characteristics: Known for its wiry, flexible branches, this tree or shrub can reach heights of about 5 meters. It has small, grey-green phyllodes instead of leaves, and its flowers are yellow. The wood is incredibly tough and was used by Indigenous Australians for making tools and weapons.
- Distribution: Found in the arid and semi-arid regions of Australia, particularly in the northern part of the continent.