Gardening with the enemy

Published Mar 1, 2013


Johannesburg - Britain has just issued its first list of banned invasive species. The list contains 69 animals and 56 plants that can no longer be sold in UK garden centres, propagated, reared or dumped illegally.

The UK has 1 798 exotic or alien plants in the country and Britain’s environment minister, Richard Benyon, said tackling the impact of invasive species cost £1.7 billion (R23.5bn) each year. The new legislation takes effect in April next year. From this date, UK garden centres and pet stores will have to stop selling these species or face a fine of up to £5 000 and possibly up to six months in prison.

Six of the invader species on the UK banned list are South African. Top of the list is the indigenous crocosmia or montbretia (Crocosmia x crocosmiiflora).

Other South African species on the UK list include the succulent ice plant (Carpobrotus edulis), African clawed toad (Xenopus laevis), giant kelp (Macrocystis angustifolia) and oxygen weed or curly waterweed (Lagarosiphon major).

The common barn owl (Tyto alba), which is indigenous to South Africa and Europe, is also on the list and may not be reared, traded in or imported.

The banning of South Africa’s indigenous crocosmia in the UK follows the listing of crocosmia as a prohibited species by the California Invasive Plant Council in 2006.

California has 4 800 indigenous plant species and an estimated 1 800 exotic or alien plants. Less than 200 of these exotics are deemed to be a threat to the local ecosystems and are ranked as high, medium or limited threats to ecosystems in the state.

By far the most threatening South African invader in California is the ice plant (Carpobrotus edulis). Crocosmia and the African wild olive are deemed to be only a limited threat, while the pink winter Cape oxalis (Oxalis pes-caprae) is listed as a moderate threat.

The National Pest Plant Accord (2001) lists about 150 exotic or alien invader plants, all of which may not, by law, be sold, propagated or distributed in New Zealand.

Indigenous South African garden plants that appear on the New Zealand Pest Plant Accord list include the ice plant (Carpobrotus edulis), mickey mouse plant (Ochna serrulata), pig’s ear (Cotyledon orbiculata), fairy crassula (Crassula multicava), plectranthus (Plectranthus cilliatus), sweet pea bush (Polygala myrtifolia), Cape tulip (Moraea flaccida) and oxygen weed (Lagarosiphon major).

Although the standard white arum does not make the list, the spectacular green goddess arum (Zantedeschia aethiopica), a marbled green and white hybrid, feature on the invasive list in New Zealand where it is deemed to be a troublesome nuisance.

Australia has various levels of invasive plant species legislation. There are no South African species in their six worst plants that demand compulsory removal.

However, under the Weeds of National Significance legislation passed in 1999, a further 32 national invaders were identified that cannot be grown, propagated or traded. Two South African plants, asparagus fern and KwaZulu-Natal’s coastal boneseed shrub or bitou bush, feature on this important national list.

Known to Australians as bridal creeper, the asparagus fern (Asparagus asparagoides) arrived there with the floriculture industry 120 years ago and is regarded as the of the most serious environmental weeds of southern Australia.

The tubers of the bridal creeper form an impenetrable mat of foliage 5-10cm deep in the forests around Adelaide. This mat is contributing to the extinction of several indigenous Australian ground orchid and forest shrub species.

Australia’s individual states also list invasive plants that pose a challenge to various regions. Among these lists are a host of Cape bulbs and tubers, including freesia, babiana, Homeria elegans, Cape moraea, watsonia, flame lily and white arum.

Other South African species declared as invasive include the African olive (Olea africana subsp. africana), Karoo thorn (Acacia karoo), African lovegrass (Eragrostis curvula), the 5m South African blue psoralea (Psoralea pinnata), Cape oxalis (Oxalis pes-caprae) and umbrella sedge (Cyperus involucratus).

Why are these South Africans deemed to be a problem? White arums (Zantedeschia aethiopica) are a noxious invasive alien weed in Western Australia (all parts of the plant are toxic). They are a big problem to the south of Perth around the Margaret River where they have taken over pasture space and become a danger to livestock.

Known to Australians as the “glory lily” the South African flame lily (Gloriosa superba) forms dense thickets on the coast dunes of south-east Queensland, New South Wales and Victoria. It is also known to be poisonous.

Six species of South African watsonia are regarded as garden escapees. Their worst invasion is to be seen in the conservation area of Kings Park in central Perth. - Saturday Star

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