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Trees of the Bay Area

Black Acacia

Black Acacia

Acacia melanoxylon

John Doyen, Tony Wolcott

This article appeared in the 2014 March issue of Chips & Chatter.

This tree goes by many common names, but as an arborist and plant enthusiasts would agree this trees is best known as a pest – on the Cal-IPC list as an invasive weed. That means this tree has naturalized, seeds readily and crowds out other plants. 

There are a few good things about this tree. The wood is hard and strong, can be milled and turned with a lustrous finish. You will have to sharpen your tools often as black acacia seems to be part rock. Table tops and other slabbed usages can be spectacular as the grain is course, sometimes cross grained, or wavy. Fine figure can be found. The wood will vary in color, yellowish sapwood, reddish brown heartwood with black streaks and quite variable, some wood reminiscent of walnut. Turning is a challenge and a chore but a nice finished ending. You will see some heart checking immediately and surface checking through the drying stages, but not deep and fairly stable wood.

There is an interesting aspect to Acacia melanoxylon as it grows. First, this tree is from Australia, a broad leaf evergreen (Angiosperm), belongs to the Fabaceae family, one of the largest families capable of providing its own nitrogen supply through fungal symbiosis. Acacia is the largest tree genus, over 1200 species. Black acacia produces a bipinnately compound leaf at first flush of growth, and then quickly converts over to a flattened leathery phyllode. It reminds me of pollywogs and frogs, not quite the same as juvenile eucalyptus leaves which is replaced by a mature leaf such as the silver dollar eucalyptus – a mainstay in flower arrangements. This type of conversion makes seedlings and saplings easy to identify as Acacia melanoxylon. Now that you know you are under an ethical mandate to pull this weed out when you see it. Don’t worry there will always be black acacia to pester us. Arborists get together for pith pulling parties just to help our riparian areas, because that little seedling or root sucker or stump sprouter is the pith. 

On a scale of 1 to 10, ten being the worst. Black Acacia comes out a robust ten for allergenic plants. The leaves are poisonous. In the Bay Area it is said that no matter where you stand you are 100 yards from at least one rat, the same can be said for Acacia mel- anoxylon. At the corner of Monroe and San Pablo Avenue in Albany on the west side of San Pablo and both sides of Monroe, there are approximately 20 black acacias, quite mature.