Acacia crassicarpa

tree in full flower


Acacia crassicarpa

Benth. 1842

pronounced: uh-KAY-shuh krass-ih-KAR-puh

(Mimosaceae — the wattle family)

common name: thick-podded salwood

native 4Acacia comes from the Greek ακις (akis), a thorn or spike; crassicarpa is from a Latin word, crassus, thick, and a Greek one, καρπος (karpos), a fruit. Salwood is from sallow-wood, sallow being a willow, especially one of the broader-leafed kinds with comparatively brittle twigs; the word sallow derives from salix, the Latin word for a willow.

Acacia crassicarpa occurs in northern Queensland, the Torres Strait islands, and New Guinea. In Queensland it extends down the eastern coast as far as Townsville, with odd occurrences in the Burdekin area, the Whitsundays, and near Mackay. It is most common on sandy, lowland, coastal or near-coastal sites, where it is found on sandy levees near seasonally dry creeks, and on coastal foredune systems. One of these trees is growing just inland from the creek at the northern end of Picnic Bay, by the side of the overgrown path that leads from the end of Magnetic Street, through the mangroves, to the beach. A line of these trees has recently been planted near the perimeter fence of the recreational camp on the outskirts of Picnic Bay, and these are growing into fine specimens.

Throughout its range the species is variable in habit and the size of its phyllodes and pods. The falcate phyllodes vary from 11 to 20 cm in length, and have about 7 veins more prominent than the rest. The prominently striated woody pods are ovoid-oblong, flat, 5 – 8 by 2 – 4 cm, glabrous, dull brown, transversely veined. The seeds are obloid, black, arranged separately in separate compartments and their arils are pale creamy yellow. The trees are usually between 6 and 25 m tall, but some grow to 30 m. On coastal dunes they tend to be shrubs, sometimes less than 1 m tall. The bark is deeply cracked.

The inflorescence is a bright yellow spike, 4 – 7 cm long, clustered in groups of 2 – 6 or so in the upper axils. The flowers are bisexual. Flowering starts as early as 6 months after the tree is established, and seed is produced in abundance after 4 years. The seeds mature 5 – 6 months after flowering. In its native range, the main flowering season is May – June, but light flowering may occur as late as September. The peak fruiting season is October – November; but there is considerable variation between locations and from year to year.

This tree is a vigorous nitrogen-fixer and nodulates well. The leaves decompose slowly, and are useful as mulch. The wood from the tree dries out moderately quickly and is useful for firewood and charcoal. It also makes good wood-pulp, better from the softer wood of plantation-grown trees than from the native ones. The sapwood is pale yellowish brown and the heartwood golden brown. The wood is suitable for a wide range of sawn-timber end uses, for light construction, furniture, flooring and boat-building.

The tree is a food plant for the caterpillars of the Northern Imperial Blue or Northern Hairstreak butterfly, Jalmenus eichhorni.

Photographs taken at Picnic Bay 2009, 2013
Page last updated 28th June 2018