From the grass on our lawns to the food on our plates, most of the plants around us are introduced species. Many don't cause any problems, but there are some with particularly nasty characteristics which have grown out of control and become weeds.
In Victoria, weeds were introduced both accidentally and deliberately. In some cases, unwanted seeds contaminated imported crops and spread wildly on arrival. Other plants were introduced for a particular purpose – for example, to re-create a foreign garden style – but became pests when they invaded the surrounding landscape uncontrollably:
A plant may become a weed as the result of the spread of cultivation owing to its excessive powers of reproduction and maintenance, coupled with some obnoxious peculiarity.
– Alfred J Ewart, The Weeds, Poison Plants and Naturalized Aliens of Victoria 1909
Ewart, A.J. 1909, The weeds, poison plants and naturalized aliens of Victoria, J Kemp, Government Printer, Melbourne, Vic.
Old sources often use very formal language, so it's useful to start your research with contemporary secondary sources, which are easier to read and give the most recent interpretation of the topic.
The infamous thistle first appeared on squatting runs in the 1840s, and by the 1860s had become a widespread problem across Victoria. It became such a pest that in the 1890s, the government introduced laws forcing landowners to control it. The government botanist, Ferdinand von Mueller, was even commissioned to write a book that identified the different kinds of thistles.
Interestingly, Victoria's most hated weed, the blackberry, was introduced on purpose. In 1858, von Mueller began cultivating blackberries at the Melbourne Botanic Gardens, and scattered their seeds in the bush, not knowing how wildly they would grow. The blackberry's thick, prickly growth has since been almost impossible to stop, and provides a haven for introduced animals, such as rabbits.
Gorse is another pest plant in Victoria: originally introduced to form prickly hedge fences, it quickly grew out of control. African boxthorn was also originally a hedge plant, but now grows into large bushes with prickles about 75 mm long. It is difficult to destroy and is another handy hiding place for rabbits.
Victoria has a long list of introduced plants that are now considered weeds, and new ones are still being added. Some species became invasive pests in the 19th century and are still a problem today.