Arum or calla lily (Zantedeschia aethiopica )
An erect perennial herb to about 1m high, which forms large clumps over time. Leaves are very large (to 60cm long), glossy, dark green and arrowhead-shaped. Flowers consist of a large (to 25cm long) white sheath enclosing a yellow spike. The fruit is a cluster of swollen orange berries enclosed in the remains of the sheath. The cultivar 'Green Goddess' has a flower sheath which is green towards the top.
Preferred habitat and impacts:
Moist sunny situations such as creek banks and swamp edges are preferred but arum lily also tolerates full shade. It can invade pasture in moist sites.
It forms dense stands which smother all native groundcover vegetation, prevent regeneration of trees and shrubs and eliminate habitat for native fauna.
All Zantedeschia species are highly poisonous when eaten raw. They are known to have caused the deaths of cattle and children. All parts of the plant are toxic, and produce irritation and swelling of the mouth and throat, acute vomiting and diarrhoea.
Clumps spread gradually from underground rhizomes. These could be washed out and spread down rivers by floods. Dumping of garden waste could also spread the plant vegetatively. Seed is spread by birds and foxes, water and in contaminated soil or dumped garden waste.
There are some similar native plants with arrowhead-shaped leaves and the flowers consisting of a spike enclosed in a sheath. Cunjevoi (Alocasia brisbanensis) grows from 1-1.8m high and the green flower sheath is more slender, and constricted about a third of the way up from the base, unlike the uniformly flared arum lily Cunjevoi only grows naturally north from the Illawarra, generally on rainforest margins. A smaller plant is Typhonium eliosurum, a rare species growing on rainforest margins and creek banks north from Nowra. Its leaves are arrowhead-shaped but with the leaf constricted near the base so that it forms three distinct lobes. The sheath around the flowers is green to greenish-purple, not white.
Another weed in the Araceae family is taro or elephant ears (Colocasia esculenta) which forms similar spreading clumps to arum lily, but has the leaf stalk attached to the back of the leaf partway up the leaf surface, rather than at the base. Its flower sheath is green at the base becoming yellow. Another arum lily (Arum italicum) has leaves marbled with white and the flower sheath green at the base. Both these species naturalise and should be controlled as for Zantedeschia.
There are additional cultivars and species of arum or calla lily (Z. aethiopica hybrids, Z. rehmannii and Z. elliottiana). The latter have pink or yellow flower sheaths and white spotted leaves. They are less hardy than Z. aethiopica and may be less likely to naturalise in cooler climates. However, any cultivars with Z. aethiopica in their parentage should be avoided.
Small infestations can be dug out, but all of the rhizome must be removed and destroyed off-site, as plants left lying on the soil surface make take root again, and any rhizome left in the ground will regrow. Herbicides will kill arum lily, but repeat applications over 2-3 years may be needed. Surfactants will improve penetration into the waxy-coated leaves. Seed is short-lived in the soil, so once parent plants are eliminated there should be no further seedling production.
If treating riverbank infestations, it will be necessary to plant native vegetation after treatment, to prevent erosion. Consult with the Department of Land and Water Conservation before commencing any removal of vegetation on river banks. Remember that there are restrictions on the use of herbicides in watercourses.