Acacia Plant Types: How Many Varieties Of Acacia Tree Are There
Acacia trees, like beans and honey locust, have a magical power. They are legumes and can fix nitrogen in soil. Known as wattle in Australia, there are about 160 different varieties of Acacia, most with fine, feathery leaves and beautiful floral displays. We’ll go over the different Acacia trees that are most popular, so you can decide which is right for your landscape.
Australian Acacia Varieties
Acacia are trees to shrubs and closely associated with Australia, although they do grow in other warm regions. Acacia are members of the pea family but don’t resemble those legumes at all. Most of the Acacia plant types have similar leaves but some have modified forms called phyllodes. There are also variable flower colors and some forms have thorns while others do not.
The “wattles” of Australia span the country. The most commonly known is the Acacia senegal, which produces acacia gum, a compound used in numerous applications from food to pharmaceuticals and even into building materials.
Some forms with phyllodes are Gold Dust wattle, Wallangara wattle and Hairy Pod wattle. There are also varieties of Acacia with true leaves such as Green wattle, Deane’s wattle and Mudgee wattle.
The forms range from the lovely weeping Hairy wattle shrub to the Blackwood, which can reach 98 feet (30 m.) in height. Most Australian types of Acacia are medium to large shrubs with thorns, although thornless varieties also abound.
Other Acacia Varieties
Many tropical to subtropical regions have endemic populations of Acacia. Acacia moa is native to the Hawaiian Islands, and its wood is used for guitars, canoes and surfboards.
A South American native, Espinillo, is a small shrub with delightful pompom-like bright yellow flowers. The Umbrella Thorn is found in African savannahs, while Sweet Acacia has naturalized in parts of California.
A symbiotic relationship exists between ants and the Whistling Thorn. They colonize the interior of the large thorns and live inside the protective embrace of the spines. Thorns emptied of ants make the characteristic whistling noise when wind passes through them.
Ornamental Acacia Plant Types
There are so many different Acacia trees that it would take a small novel to list them all. Some types of Acacia are really only suitable for reclamation, wild habitat and large, open spaces, but a few are really so pretty you might want them in your garden.
‘Limelight‘ is a compact shrub with a slightly weeping habit and lush foliage. Similarly, ‘Fettuccini‘ has drooping leaves but can also be found in a really astounding standard little tree form.
For interesting flower color, ‘Scarlett Blaze‘ has orange-red blooms. The Coast wattle has interesting bottle-brush blooms, Blue leaf wattle boasts blue-green foliage and bright yellow pea-like flowers, while Juniper wattle bears needle-like leaves and cute little white puffs of blooms. Oven’s wattle is a weeping variety with deeply gold flowers and received the Award of Garden Merit.
As you can see, there is an Acacia for nearly every garden situation.
While on safari in Tanzania you will not only see animals, but also trees. Tanzania has hundreds of tree species but today I am highlighting one in particular, the acacia family. East Africa has around 62 species of which six are endemic to Tanzania. Acacias can grow as trees and shrubs, but the most classic acacia trees seen on safari include the umbrella tree, whistling thorn, wait-a-bit acacia and the yellow fever tree.
The umbrella tree has become almost a symbol of the African bush. It is always photographed as the most typical tree in African bush. Ask a person to think about the first tree that comes to mind, when you say ‘the African bush’? They will most probably mention the umbrella tree, envisioning a lone tree in front of a tremendous sunset.
The Serengeti National Park is a protected area that covers thousands of square kilometers and it is the habitat of several species of acacia trees. These trees are quite formidable and adapt well to their surroundings. Each species has special characteristics, but most of them have one thing in common; their defense mechanism – thorns.
Acacias are often referred to as thorn trees. Some have long straight thorns while others have hook-shaped ones. The main reason is that it acts as a deterrent against browsers. Scientists have said that despite the thorns, some herbivores still feed on the trees. Not preventing feeding, but indeed limiting over-grazing. One interesting fact is that when browsed on by, for example giraffes, some acacia trees release a toxin known as tannin. This makes the leaves inedible and causes the animal to seek ‘greener pastures’. The toxin can be quite dangerous to the animals if ingested and can be lethal.
A zoologist from South Africa, Wouter Van Hoven found that acacia trees also have another chemical defense system, whereby they release a chemical called ethylene. This chemical can travel up to 45m, ‘warning’ other acacias in the vicinity. Within 15 minutes all the neighbouring trees increase the tannin levels in their leaves, making the area pretty unappetizing to tree-browsing animals.
In order to ensure enough food, giraffes tend to eat downwind from trees, in the hope that the trees do not alarm each other. They also usually browse only for a short time before moving on to the next tree.
Another incredible defense mechanism is that acacia trees have ‘body guards’ in the form of biting ants. The whistling thorn is a good example of this; at the base of the thorns is a hollow bulb. These bulbs provide shelter for the ants and the tree provides plenty to eat in the form of nectar and sap. The ants return the favour by attacking any herbivore that tries to eat the leaves.
Next time you see an acacia tree don’t just think of it as a tree but rather a tree that is actually quite clever.
Acacia is a very large genus of plants in the family Mimosaceae, a subfamily of the Fabaceae or Pea family. Acacia species are found throughout the world; however most of the species that are cultivated in California come from Australia. There are many diverse forms within the genus. These range from large trees to prostrate shrubs. Many of the plants in cultivation are noted for their form, foliage color, flowering accent, adaptability and cultural tolerances. In many cases all of these attributes combine to make an exceptionally attractive and useful plant.
There are several cultural considerations when planting Acacia.
It is wise to select the appropriate plant for a given situation but in many cases the ultimate form of an Acacia is determined by pruning; a large shrub species can be trained into a small tree or a tree species can become a shrub. To form shrubs out of trees, top out the main leader; to create a tree from a shrub, prune out the side branches and stake. Shaded branches tend to dieback and should be pruned out. Pruning to open an acacia shrub or tree will minimize this as well as produce sturdier branches which will prevent wind damage – deadwood is easily felled by strong winds.
Acacias can withstand a fair amount of cold weather, but most cannot tolerate long periods below 20 ° F.
Irrigation and Fertilizing
Newly planted Acacias require an infrequent yet deep watering to produce a well anchored, deeply rooted plant. Once established; usually within the first year in the ground, most Acacia can thrive with just rainfall and a few deep waterings. More frequent watering can promote root rot which can kill otherwise healthy plants. Acacia do not require heavy amounts of fertilizer and in some cases can be harmed by the addition of fertilizers high in phosphorus.
In general Acacias are relatively short lived, lasting anywhere from 20-40 years though older specimens of some species, such as Black Acacia (Acacia melanoxylon) are noted in the wild and in cultivation. This short life span is often compensated for by rapid growth and youthful vigor. Acacias also will often flower within their second year so by the time a tree or shrub is planted it is usually of flowering age.
The following Acacia are grown at San Marcos Growers:
Acacia adunca – Wallangara Wattle
Native to Queensland and New South Wales. Fast-growing, small (to 23 feet tall) tree with slightly weeping branches and long, dark dull green leaves and fragrant yellow flowers that form in terminal clusters winter through early spring. Requires full sun and good drainage for its best growth; will grow in part shade. Frost and fairly drought tolerant once established. (We are currently not growing this plant)
Acacia baileyana – Fernleaf Acacia
Native to New South Wales. A fast-growing small (20-30 feet tall) tree with silvery gray/blue gray, feathery leaves, wide-spreading (20-40 feet) canopy, and weeping branches. Bright golden yellow small rounded flowers bloom late winter through early spring. Requires full sun to filtered shade, well-draining soil and regular watering for its best appearance. Not fussy about soil type. Once established it is frost and moderately drought tolerant.
Acacia baileyana ‘Purpurea’ – Fernleaf Acacia
Similar cultural and growth habits as A. baileyana other than the new growth has a purple tinge to it and its canopy is not as wide-spreading.
Acacia boormanii – Snowy River Wattle
Native to New South Wales and Victoria. A fast-growing multi-stemmed shrub to 16 feet tall. Composed of thin, graceful, silvery stems/branches and small, narrow gray-green leaves that are evenly spaced along the branches giving the plant a light feeling. Bright yellow rounded flowers form in clusters in early spring. Very tolerant of cold, it will withstand some drought, but looks better if placed on a regular watering schedule. Plant in full sun to filtered shade. Requires good drainage. A great specimen plant to bring in the vertical plane of your garden plan; noticeable, but not overpowering, it can be used with many other plants to bring out their unique characteristics.
Acacia cognota – River Wattle
Native to Australia. A quick-growing, small (20-30 feet tall), graceful tree or shrub with narrow, drooping bright green leaves and weeping branches. Small rounded yellow flowers appear in pairs in spring. Requires full sun to light shade and very good draining soil. Protect from salt-laden air along the coast and hot sun inland.
Acacia cognota Cousin Itt – Little River Wattle
Native to Australia. A dwarf selection of a tree forming species that get 2-3 feet tall with narrow, drooping bright green leaves and weeping branches. Requires full sun to light shade and very good draining soil. Protect from salt-laden air along the coast and hot sun inland.
Acacia covenyi – Blue Bush
A fast growing shrub or small tree to 20 feet tall from Southern New South Wales, Australia with dark brown stems and silver-blue 1 to 2 inch long elliptic leaves (phyllodes). In spring appear the ½ wide globular bright yellow flower heads that are held in upright racemes about the length of the phyllodes. Plant in full sun in a well drained soil. Requires little to no irrigation. Tolerates hard frosts and temperatures below 15° F.
Acacia craspedocarpa – Leather-leaf Acacia
Dense, rounded shrub to 8 feet tall by 5 feet wide with leathery 1 inch long broadly elliptical gray leaves (phyllodes) finely netted in green. The stems and new growth have coppery tones and the bark is somewhat fissured. The flowers in short, golden spikes (rods) appear in spring and various times through the year and are followed by attractive flat, rounded bright green seed pods. It is very drought tolerant once established but also tolerates regular irrigation in well drained soils. Cold hardy to 15° F. Some sources in the desert southwest list it as a tree to 15-20 feet but it is so slow growing here along the coast that this is hard to imagine. It is an interesting small tree or shrub for a low screen. Plant not currently in production
Acacia cultriformis – Knifeleaf Acacia
Native to Queensland and New South Wales. A drought resistant bushy shrub growing to a little over 13 feet tall, and as wide. 1 inch long gray-green triangular leaves tightly hug the drooping gray branches. Fragrant bright yellow rounded flowers form in clusters in spring. Not fussy about soil type, but it requires good drainage. Plant in full sun to light shade. Frost resistant. Foliage can be used in flower arrangements. An unusual plant for its leaf-shape and color. Can be used as a specimen; in a mixed drought garden; as a hedge or screen.
Acacia glaucoptera – Clay Wattle
Native to Western Australia. A highly unusual acacia that can be used selectively as a ground cover in a small area. Growing to a little over 3 feet high, it has a sprawling habit; twisting branches clothed with continuously overlapping, flat pointed, gray-green leaves giving the appearance of a zigzagging stem (think of what is commonly depicted as a dragon’s back). The new growth of this acacia is red or bronze; and in the cooler months the foliaged stems take on an almost purple tone. Large, rounded yellow flowers form along the stems in spring. Grows in full sun to light/filtered shade. Requires very good draining soil. A good plant for under open trees. Prune back if it becomes straggly looking. An oddity in the garden, it nevertheless, will always command a viewer’s attention, wonderment and praise. Plant not currently in production
Acacia iteaphylla – Willow Acacia
A dense tall shrub to 10-13 feet tall with intricate angular branching structure and somewhat drooping tips and bearing many soft narrow blue-green leaves (phyllodes) Stems and leaves are have a distinct red tinge when young. Pale yellow fragrant flowers emerge in late winter to early spring. A very adaptable shrub that tolerates most soils. Noted to be drought and lime tolerant and tolerant of coastal planting outside of severe exposure to salt spray.
Acacia longifolia – Golden Wattle
Native to New South Wales, Victoria, Tasmania and Southern Australia. A very hardy, fast-growing bushy shrub/small tree to a little over 16 feet tall, and as wide. Long (3-6 inches), light green leaves and fragrant round, golden yellow flowers that form along the plant’s branches in winter/early spring make up this plant’s appearance. While very adaptable to soil types it does require good drainage. Plant in full sun to light shade. A good plant for seaside conditions. Frost and drought resistant. Use as a screen, windbreak or quick coverage of an unsightly object. Used a lot in the freeway plantings of southern California.
Acacia melanoxylon – Black Acacia
Native to Queensland, New South Wales, Victoria, Tasmania and South Australia. A very quick-growing, pyramidal tree growing to almost 40 feet tall and 20 feet wide, with a straight, vertical trunk and long (2-4 inches) dark gray-green leaves. Creamy flower clusters form in winter and spring. Plant in full sun to filtered shade. Should have a deep soil that drains well. A good tree for erosion control. Be cautious in using this tree as it has aggressive roots and can lift sidewalks or damage foundations if planted too closely. Its branches are considered brittle and the plant suckers easily.
Acacia merinthophora – Weeping Myall
An open shrub reaching 9 to 12 feet tall with a weeping habit from Western Australia. The phyllodes are long (up to 8 inches), curved , narrow and are gray-green in color. The stems of the branches change direction at the points where the phyllodes occur producing a zigzag shape. The branches are very attractive in dried arrangements. Short, rod-shaped flower clusters (about 1-2 inches long) are produced in the phyllode axils in early winter to early spring. They are bright yellow in color and are followed by slender, curved seed pods. Although native to Western Australia, Acacia merinthophora has been successfully cultivated in humid areas where many other western species fail. It is best grown in a well-drained, sunny position and, once established, will tolerate extended dry periods. Cold hardy to 25-30° F, possibly lower once established. The botanical name aacia; is from Greek acis, a thorn. The specific epithet, merinthophora; with long, thin phyllodes.
Acacia pendula – Weeping Myall
Native to Queensland, New South Wales and Victoria. A small, slow-growing tree to almost 40 feet tall in its native habitat, usually to around 25’x 15′ in most gardens, with weeping branches clothed in narrow, 2-3 inch long, silvery blue-gray leaves. 1/4 inch wide pale lemon flowers appear irregularly. Drought resistant, but the soil should be slightly fertile and well-draining with some moisture. An excellent choice for a drought tolerant garden, mixed with grasses and phormiums, rock gardens and as an accent plant. Plant not currently in production
Acacia podalyriifolia – Pearl Acacia
Native to Queensland and New South Wales, Australia where it is commonly called Queensland Silver Wattle or Mount Morgan Wattle. A small tree or medium to large shrub to 15 feet tall by nearly as wide. The soft gray rounded phyllodes have a conspicuous central vein. Bears masses of bright yellow fragrant flowers in late winter. Needs good drainage to perform well. Responds well to heavy pruning after flowering. A very beautiful Acacia.
Acacia redolens – Prostrate Acacia
A low-growing acacia that is readily used as a groundcover, especially on slopes. Grows to 3-5 feet tall and 15 feet wide. Dense, the plant is heavily branched and covered with narrow, gray-green leathery leaves. Small yellow flowers appear in spring. Plant in full sun to light shade. Not fussy about soil type, but requires that it be good draining. Tolerant of drought and frost once established. Plant not currently in production and only growing the variety ‘Low Boy’
Acacia redolens ‘Low Boy’ – Low Boy Prostrate Acacia
A selected very low-growing prostrate acacia that stays under 1 foot tall. This cutting grown plant is vastly superior to the seedling grown plants commonly found. A good groundcover, especially on slopes. As with the species it can grows 15 feet wide. Dense, the plant is heavily branched and covered with narrow, gray-green leathery leaves. Small yellow flowers appear in spring. Plant in full sun to light shade. Not fussy about soil type, but requires that it be good draining. Tolerant of drought and frost once established.
Acacia stenophylla – Shoe-string Acacia
An open, quick-growing tree to 30 feet tall by 20 feet wide. Very long (to 16 inches), narrow and slightly twisted drooping leaves lightly clothe pendulous branches. New bark is maroon. Small, rounded creamy yellow flowers appear in late winter/spring followed by clusters of pendulous chocolate brown seed pods. A wonderful tree for light shade; for a mixed succulent/drought tolerant garden; for the unusual shadows cast by its structure. Drought and frost tolerant once it is established. Plant in full sun to light shade in deep, well-draining soil. Stake until it is deeply rooted.
Acacia vestita – Hairy Wattle
A dense growing tall shrub to 12-15 feet tall by equal spread. The long pendulous branches are covered with oval soft pubescent gray green leaves. The golden yellow flowers are held in clusters at the branch tips in the spring. A very adaptable shrub which tolerates both short periods of soggy soil and dry periods. Prune carefully so not to destroy the beauty of the pendulous branches.