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Rhus Tree

Rhus leaf tip

Rhus leaves & fruit

Rhus leaf underside

Chinese pistachio leaf

Chinese pistachio fruits

Toona red cedar leaf

White cedar leaf

White cedar fruit



Family:

Anacardiaceae


Status:

Rhus is declared noxious in class 4  in all NSW LCAs. Rhus is a declared noxious weed in NSW because of the health risk it poses to humans. It is illegal to grow it or sell it.

Description

Rhus (Rhus succedanea, formerly Toxicodendron succedaneum) is a deciduous small tree to 5-8m high with smooth, grey bark. It has compound leaves to 10-30cm long with 4-7 pairs of leaflets. There is an unpaired terminal leaflet at the tip of each leaf. Each leaflet has a long tapered tip and a rounded asymmetric base. The leaflet lower surface has a slight whitish bloom. Tiny yellowish flowers are carried in large clusters 8-15cm long. The 5-11mm wide fruits are round but slightly flattened in one plane, pale brown and hard textured with a papery skin. They hang in clusters on the tree through winter, falling in spring.
The sap of rhus is highly toxic. It is closely related to the North American poison ivy and poison oak. First contact with the plant may not produce any effects but sensitivity develops with further contact. Usual effects are severe dermatitis, with a rash and blistering coming on within 1-7 days of contact and persisting for 10-14 days. Hospitalisation may be required.
All parts of the plant are poisonous and in highly sensitive people merely standing under it may be sufficient to produce a reaction. Contact with dried sap on clothing or tools is just as dangerous, and the sap may remain active for months. While some people react to it immediately almost everyone will develop a sensitivity to Rhus after sufficient exposure.

Dispersal

Seed is spread by birds. Rhus used to be popular because of its brilliant red autumn colour, but is no longer sold because of its toxic properties. However, it is still found in some gardens and birds can spread the seeds into bush, or into your garden without your knowledge. The seeds are produced in large numbers and are said to have a high germination rate, so this plant has high weed potential.

Look-alikes

Another exotic, Chinese pistachio (Pistacia chinensis) is similar and is sometimes recommended as an alternative small tree producing good autumn colour (usually red or orange). It also is weedy, with the small red to purple soft fruits being spread by birds. It has shown considerable ability to spread into native vegetation in the cooler climates of the NSW tablelands and Blue Mountains, where it has possibly been planted for longer than it has on the coast. It is distinguished from Rhus by having leaves which mostly lack a single terminal leaflet. Apart from this they are similar, being 10-25cm long, with 4-7 pairs of leaflets, each with a tapered tip and asymmetric base. The leaf underside does not have a whitish bloom. The fruits are held in clusters on the tree after the leaves fall. The clusters have stiffer branches than those of Rhus, whose fruits droop more.

A few native rainforest trees such as scentless rosewood (Synoum glandulosum), which grows north from Bega, and ribbonwood (Euroschinus falcata), which grows north from Jervis Bay, have similar compound leaves and berry-like fruits. However, they do not change colour in autumn or lose their leaves in winter. Red cedar (Toona ciliata) is a native tree which is deciduous and has compound leaves, but they usually have no terminal leaflet (except occasionally in young growth) and the leaf is larger (15-45cm long) with 4-10 leaflet pairs.

White cedar (Melia azedarach) is a deciduous native tree which also retains its fruits on the tree through winter. The fruits are larger than those of rhus (up to 2cm diameter) and are cream colored. The leaves of white cedar are bipinnate, that is, at least some of the leaflets are themselves further divided into leaflets. The flowers are mauve and produced in large showy clusters. White cedar grows naturally on the coast north from Milton but has also been widely planted and occasionally naturalises. Its fruits are poisonous.

Control

As might be imagined, extreme care is needed when removing rhus trees. It should be done in winter when sap flow is reduced. Prevent sap from getting on the skin by covering up as much s possible with overalls, gloves and face protection. All clothes and tools which might be contaminated should be thoroughly washed in such a way that they cannot contaminate other clothing. It would be safer to poison the tree by stem injection when it is actively growing in summer (still taking precautions to avoid the sap) and cut it down once it is long dead. If live trees are cut the stump should be painted with herbicide to inhibit re-sprouting. If a brush is used for this task, bag it securely and dispose of it safely.

Do not chip any material as even the dried sap is toxic for long periods, and do not burn it as the smoke is highly toxic. Seedlings can be dug or chipped out. Wear rubber gloves when dealing with them.

Chinese pistachio can be cut and painted or stem injected without such precautions.