Family: Fabaceae (peas)

Status:

Description:
A fast-growing deciduous tree to about 20 m high. Bark is rough and furrowed on trunk and larger branches. There may be small triangular thorns on the smaller branches. Leaves are compound, to about 15cm long, with 10-20 leaflets in opposite pairs and a single terminal leaflet which is larger than the others. The leaves are thin-textured and bright green with a paler, whitish underside. Clusters of pure white pea flowers occur in spring. The seeds are black, hard-coated and are contained in a flattened bean-like pod, 3-8cm long.

Preferred habitat and impacts:
Usually found only where it has been planted, close to towns or farm buildings. Forms dense thickets by root suckering, which can exclude all other vegetation.

The bark, roots, wood, seeds and pods are poisonous.

Dispersal:
Seed could be spread by water, or by large birds such as cockatoos, but the main means of reproduction is by root suckers. One plant can become a large thicket. Root fragments could be spread by machinery.

Look-alikes:
There are no similar natives. Although red cedar (Toona ciliata) is deciduous and has compound leaves, its leaves are much larger and softly hairy, and it lacks the conspicuous sprays of white pea flowers.

Honey locust (Gleditsia triacanthos) is a similar exotic tree, distinguished by its long three-pointed or branched thorns and longer (up to 30cm) strap-like seed pods. Thornless varieties of this species, sometimes with yellow or purple-tinged foliage are sold in nurseries. Honey locust seems less prone to suckering than black locust, but can be spread by seed. It is occasionally found far from buildings in remnant native vegetation in farming areas. It prefers open, sunny situations.

There are various other Robinia species available from nurseries, usually grafted onto black locust rootstock.. They have pink, cream or white flowers and similar leaves to black locust. Most of these are also prone to suckering, and should only be planted in situations where the roots will not be disturbed (for example by foot traffic or cultivation nearby) and where suckering can be controlled by mowing.

Control:
Don’t plant black locust or grafted Robinia as an ornamental or shade tree. Root suckers can be suppressed by regular mowing or grazing, but will develop into trees if these restraints are removed. Once a thicket exists it will be necessary to stem inject or cut and paint all stems. It is not likely to be possible to treat the suckers and have the parent tree remain, since herbicide applied to the suckers will get into the root system of the parent tree and cause it to look unhealthy, if not actually killing it.

Do not cut trees down without applying herbicide to the stump or massive suckering will result. Ploughing, or slashing of small plants, will have the same effect.