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Wednesday, March 30, 2011

Acacia melanoxylon - Black Acacia

The black acacia is almost as common, maybe more so that the silver waddle, you might just not notice it as much. They remind me of large billowy masses of medium green foliage providing an evergreen background for other trees. You only really notice them when they start to bloom.

This is perhaps one of the most invasive plants in our area. You need to be careful getting mulch from tree companies as the seeds are very viable. You really don't have to go far to see young trees of this species. Luckily they are fairly short lived.

This Acacia is a large fast growing evergreen tree growing 25 - 50' or more, can be up to 90'. Eventually forms a dense rounded canopy with an overall dull green cast.

The leaves are very different than those of most other acacias in our area and in true botanical sense they are not even leaves... (I know) but really flattened petioles (the leaf stock). The true leaves (bipinnately compound) are present when very very young or occasionally on a sprouting trunk.  So the "leaves" you normally see are 2-5" long, medium green to dark green in color, straight or curved with distinct veins running parallel (an unusual arrangement for a dicot) are really petioles.

You may find them like this picture where they are transitioning to flattened petioles (call phyllodes).

The flowers are similar to other acacia in that they are clustered into heads in a raceme but like the others around here they are very light yellow. Some trees seem to be covered while others have few. Not really attractive but nice.

One thing you will notice and want to avoid is the seed heads. The fruit is a legume (a pod opening on both margins) medium brown, constricted and twisted, with flattened black seeds. The seeds have a red aril that attract birds and help move the tree.

Bark on old trees is reddish brown and shallowly furrowed. On young trees it will be green to silver gray and smooth.

Misidentification? Look at the foliage, the leaves are slightly falcate or sickle-shaped and the veins appear parallel.

Care to mention a nice specimen?

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