By David Gress
The Shoestring Acacia earned its unusual name from its distinctively long and thin leaves that hang from its gracefully arched branches.
This picturesque tree is a relative newcomer to Santa Barbara, having become more common here in just the last 25 years. Its popularity can be attributed to its pleasing appearance and its perfect adaption to our various soils and Mediterranean climate.
The Shoestring Acacia is a medium-sized evergreen tree that is fast growing when young. At maturity, it can reach a height of 30 feet with a canopy width of 25 feet. It can also be grown as a multiple-stemmed spreading tree or large shrub. A young tree, though rather lanky at first, quickly develops a dense crown that becomes more open and sculptural over time – giving the tree a lovely, willow-like, appearance.
The crown has long arching branches, which are covered with long thin leaves (6- to 16-inches long and ¼ inch wide) that are straight or slightly curved – the “shoestrings”. The “leaves” are actually modified petioles, called phyllodes, that function like leaves for photosynthesis.
This tree has a pleasing floral display of small (up to ½ inches in diameter) creamy-white puffball-like flowers in late summer through early fall, though some flowers can be seen sporadically throughout the year. The flowers develop along the ends of branches in clusters of 3 to 5 heads called racemes Each head has 25 to 40 flowers.
Shoestring Acacia is actually a legume, as are beans, and is in the plant family, Fabaceae. It is not surprising then that its pollinated flowers develop bean-like seed pods (4- to 10-inches in length). The enclosed dark brown seeds are ¼ inches long and elliptical in shape. The pods are moniliform, meaning they are tightly constricted around the seeds and, consequently, resemble a long string of pearls. The pods are green when young and turn brown as they age and dry. The numerous seed pods dangling down from the branches are another distinctive feature of this tree.
The bark on the trunk has rusty-red furrows with light gray longitudinal plates on the ridges that blacken with age. Bark on the branches is smooth and sometimes maroon-colored.
The Shoestring Acacia is native to Australia, primarily in the eastern and central parts of the country, though smaller populations can be found in northern and southwest Australia. Its wide native range explains why it is so adaptable to various soils and climates. It is normally found in areas with a minimum of 16 inches of annual rainfall, which is similar to our normal rainfall.
The botanical name for Shoestring Acacia is Acacia stenophylla. The genus name, Acacia, is Latin but was derived from the Greek word, “akakia”, meaning “Egyptian thorn acacia”. The specific epithet, stenophylla, is a combination of the Greek words “stenos” meaning “narrow”, and “phyllon” meaning “leaf”, which refers to the narrow leaves. It has many common names in Australia, including Black Wattle, Ironwood, Native Willow, and River Cooba. In the United States, its only common name is Shoestring Acacia.
In our area, Shoestring Acacia is used exclusively as a landscape tree. Because of its widespread distribution in Australia, it has historically had many other utilitarian uses. The extremely hard wood is used for fabricating furniture and tools and for building fences. The seed pods and seeds are roasted by indigenous Australians to be used in cooking.
Shoestring Acacia should be planted in full sunlight. Some pruning might be necessary to train for structure and to reduce the number of trunks to the desired number; however, it should be thinned only when it is young. Watering is usually only needed until it is well established and during prolonged droughts. Fertilization is not necessary, because it has nitrogen-fixing nodules on its roots. It is not affected by any serious insect or disease pests. It is also very tolerant of high heat and of soils with clay and high salt content. It is cold hardy to 20 to 25 degrees F. Propagation is easy from seed. It grows quickly at first, up to 3 feet per year, but slows as it gets more mature.
The Shoestring Acacia makes an excellent drought-tolerant tree for residential and commercial landscapes. It is particularly useful on sites with poor soil. It can be planted as a single specimen for a dramatic focal point – or in groups for a grove effect. It is perfectly suited for modern lawn-free landscapes, where it can be used effectively with succulents and cactus. Planting it against a building or white wall will show off its open branching structure. It is particularly rewarding in locations where you want a quick tree.
Shoestring Acacias can be seen locally – predominantly in commercial landscapes. Mature trees can be seen at the southwest corner of State Street and De La Vina Street, at the corner of State Street and La Cumbre Road (parking area), at the northeast corner of Cliff Drive and Meigs Road, at the southeast corner of Gutierrez Street and Milpas Street (on the corner and in the back parking area) and, at the northeast corner of Chapala Street and Canon Perdido Street (in the parking area). A few can be seen as street trees at the corner of Samarkand Drive and Santa Anita Road and in the 1400 block of Lou Dillon Lane.
Tree-of-the-Month articles are sponsored by Santa Barbara Beautiful, whose many missions include the increase of public awareness and appreciation of Santa Barbara’s many outstanding trees and, in a long-time partnership with the City Parks & Recreation Department, the funding and planting of trees along the City’s streets.
Those who wish to honor a special someone can do so with an attractive commemorative marker that will be installed at the base of an existing street tree in the City of Santa Barbara. Because Santa Barbara Beautiful has participated in the planting to date of over 13,000 street trees, there are plenty of trees from which to choose! Application forms are available on the Santa Barbara Beautiful website, www.sbbeautiful.org.
Article and Photos by David Gress