Saturday, July 20, 2024

Online invasion

Many harmful, invasive plant species are let loose in the wild by careless actions of home gardeners and well-meaning professionals. There are several examples where plants were introduced to solve a problem only to become the problem. Classic example is bitou bush (Chrysanthemoides monilifera subsp. rotundata.)

According to the NSW Weedwise website, bitou bush was introduced from South Africa probably from the ballast of ships in the port of Newcastle in about 1908. From 1946-1968 bitou bush was planted deliberately along the NSW coast by the Soil Conservation Service of NSW to aid in erosion control and post-mining rehabilitation. Since then, this environmental weed has spread from Queensland to Victoria and as far west as Menindee in NSW. The total area infested is estimated currently to be over 70,000 ha in Australia.

A team at the University of Adelaide, led by Jacob Maher researched how the use of E-commerce and online trading may facilitate the unlawful spread of weeds in Australia. The Adelaide team estimates invasive species have cost Australia $200 billion since 1960. Using custom-built software, Maher and the Adelaide team searched online sales platforms for plants for sale. They particularly searched for plants that were declared as a possible invasive species and prohibited from trade. This included plants that were legally for sale in one jurisdiction but may be declared an invasive species outside their normal range. Plants legally advertised by commercial nurseries could be considered invasive in areas outside the jurisdiction in which the nursery is located but this is not illegal and is permitted.

In many cases weed risk is often included in literature accompanying the plant, for example on plant labels or pots. These are usually sold by responsible sellers.

Public E-commerce yielded many prohibited advertisements for plants prohibited for trade under jurisdictional biosecurity legislation because of their current or potential impact as an invasive species. Sellers advertise plants and sales are conducted through private exchanges either online, by phone or in person. The most frequently advertised declared plants, according to the research, were Opuntiacacti and aquatic weeds. The declared plant with the greatest number of prohibited advertisements was Opuntia microdasys (Bunny ears cactus), and other Opuntiaspecies were frequently traded, including Opuntia monocantha (Drooping prickly pear) and Opuntia ficus-indica (Indian fig). Aquatic weed species including Eichhornia crassipes (Water hyacinth) and Limnobium laevigatum (Amazon frogbit) were also traded. Zantedeschia aethiopica (arum lily), an invasive geophyte, had the highest total number of advertisements for a declared plant, and the second highest number of prohibited advertisements. Other frequently detected invasive plants were Gazania spp. (Gazanias), Hedera helix (English ivy), Lavandula stoechas (Topped lavender), Rubus fruticosus (Blackberry), Orbea variegata (Carrion flower), and Azadirachta indica (Neem). The web scraping algorithms developed by the Adelaide team also detected nineteen sale advertisements for Limnobium laevigatum in three prohibited jurisdictions.

Some sellers suggest uses to promote plants such as ‘The vigorous growth makes Privet Ligustrum vulgare a suitable screening plant and gazanias make good ground covers’. Gazania is a declared weed under the Landscape South Australia Act 2019, however there are sterile cultivars such as GT20 (Double Gold), Sugaja (Sunset Jane), and Sugamo (Montezuma) that are legal for sale.

Obviously, the online trade in plants will continue and possibly increase over time. The COVID years certainly boosted interest in indoor plants and online sales. Laws prohibiting the advertising and sale of declared invasive species of plants have not stopped the trade. The research team admit that the activity detected by their methods is probably conservative and the volume of the trade is probably much higher than their figures suggest. The report also highlights the need for cooperation between jurisdictions where plants are legally sold but may be illegally planted.

Improved enforcement of the existing law using so called ‘web scraping’ techniques could reduce some of the trade, with the recommendation by the team at Adelaide University for concerned parties to place a greater emphasis on public education and promotion of safer alternatives.


Maher J, Stringham OC, Moncayo S, Wood L, Lassaline CR, Virtue J, Cassey P (2023) Weed wide web: characterising illegal online trade of invasive plants in Australia. NeoBiota 87: 45-72.

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