Acacia longissima [Fabaceae]; Fine-leaved Wattle

After first witnessing and identifying this wattle species I was particularly excited by it. Graceful, elegant and diaphanous, and particularly luminous when backlit. But what gave me confidence for its use in landscape plantings was the incredibly generic ecological description of its habitat: “Grows in gullies on wet or dry sclerophyll forest on sandy or clay soils”. This is dream news for a horticulturist, as it implies thousands of years of evolution imbuing this species with a tolerance of wet or dry, sand and clay, and gully conditions, which are typically humid, but can also become the exact opposite in the years of long drought to which Sydney is occasionally susceptible.

In actual fact, unlike PlantNet’s habitat description, I have more often seen Acacia longissima in non-gully conditions. One example is roadsides in bushland of Ku-Ring-Gai Chase National Park, where presumably it received road rainfall runoff, simulating a wet gully –– perhaps this is a human-induced phenomenon? It is also present within Pittwater Spotted Gum Forest, an ecological community that fringes the Pittwater inlet on mixed clay-sand-sandstone soils of eroded Narrabeen Group geology.

We have planted this species in part shade on clay loam soils in small inner west courtyards and larger suburban backyards, and we know others who have done so in other conditions such as coastal harbour front in full sun. The only thing to consider is ensuring a low phosphorous content in the soil: avoid soil media that is not native-appropriate, and even be wary of various so-called ‘native mixes’ that are supplied by most landscape yards, as these can often still contain excessively elevated phosphorous, an element that is practically impossible to remove from a soil once it is in it. As with many Sydney natives, phosphorous toxicity should not be sneezed at, particularly when planting members of the families Fabaceae, Proteaceae, Rutaceae and Ericaecae. Many species in these families are so well adapted to extracting it from our low nutrient soils that they can’t survive root contact with small to moderate amounts of it.

As with most wattles, it is likely pollinated by beetles, bees and wasps.