Plant Highlight: Acacia aphylla
By Brian Kemble
Region and Taxonomy
The genus Acacia is a large one, with over 900 species presently recognized. Until 2011, several hundred additional species were included, but these were split off into other smaller genera, with the remaining species mainly native to Australia, where they are a very prominent part of the flora. Acacia belongs the the mimosoid group within the Fabaceae, or Pea Family, and this group is well known for its clusters of flowers with many long stamens. Other familiar examples include Mimosa, Albizia, and Calliandra. It is worth noting that there are many other unrelated plants with prominent showy stamens, and in Australia this would include a host of plants in the Myrtaceae, or Myrtle Family, including Eucalyptus, Callistemon, and Melaleuca. Unlike the Myrtaceae, however, the species in Acacia are strongly biased toward yellow flowers.
About the Plant
While some Australian Acacia species have long been widely used horticulturally (and in some cases have naturalized in other parts of the world), others have stayed out of the limelight. One of the latter is Acacia aphylla, a plant with a small area of occurrence near Perth in Western Australia. It is not listed in older horticultural reference works such as Hortus, but it has recently been attracting notice in California because of its unique appearance and its drought tolerance.
The term “aphylla” means “without leaves”, and indeed this interesting shrub relies entirely on its bluish-green branches for photosynthesis. There are many other acacias that possess phyllodes, where the petiole (the stalk of the leaf) has become flattened and serves the function of the blade, but Acacia aphylla has gone a step farther and dispensed with its leaves altogether. What remains is a bushy tangle of blue-green cylindrical succulent branches that curve this way and that, each one ending in a sharp tip. A plant may reach a height of up to 9 feet or a little more (2.75 m), with a spread of about 5 to 6½ feet (1.5 to 2 m). The plant’s zig-zaggy appearance and blue-green color is cause enough for admiration, but an additional layer of interest is provided by the vivid yellow puff-balls of flowers that come along in late winter to spring.
About the Inflorescence
The flowers of A. aphylla are held in round clusters atop stalks about .28 to .39 inch long (7 to 10 mm). Each cluster is a little less than a third of an inch in diameter (8 mm), and it has 20 to 30 tiny flowers that have 5 sepals and 5 petals, but these are hidden by the burst of bright yellow stamens that much exceed the petals in length. The flowers are followed by purplish-gray flattened pods that are up to 3½ inches long (9 cm) and about .14 inch wide (3.5 mm). Within are black seeds about .2 inch long (4 mm).
Care and Maintenance
Acacia aphylla needs good drainage and a sunny or part-sunny position in the garden. It is not fussy about soil pH, and it is very drought-tolerant once established. It does not take well to shearing, but it can be pruned back in spring (after it has flowered) if desired.
Click here to find out more about what’s in bloom at the Garden.