estern Australia, the Wildflower State! Not all the 'wildflowers' are truly native to Western Australia, some are migrants, and have arrived here in recent times, introduced by human beings.

There are about 10,000 named species of flowering plants growing wild in Western Australia and 90 per cent of them are natives. The other 10 per cent - about 1000 species - have been introduced to this State. This book will help you to identify these 'introduced species'.

 Human beings have brought in many plants, sometimes deliberately for crops, pastures or gardens, but also accidentally, as seeds in hay for stock feed, for example. Many of these plants would not survive without care and cultivation, but others have been able to establish and reproduce unaided. These plants are said to be 'naturalised' and most of the species described and illustrated in this book are of this type.

 Photographs and brief descriptions are given of the most common naturalised plants, others, more restricted in occurrence, are included for comparison (either in the main text or in Appendix B), but not illustrated. Where they are currently known to occur is also indicated, but new populations are constantly being recorded. If you know of a population that is not mentioned here, or even a totally new species, please make a note of it. If it is on agricultural land, please inform the Weed Science group of Agriculture Western Australia. If it is in bushland, please inform the Department of Conservation and Land Management. If it is a water weed, please inform the Water and Rivers Commission.

Why is the Australian flora so special?

Does it matter whether a plant is a newcomer to Australia, or has been evolving here in isolation for the last 50 million years? Yes, it does! It matters because these new plants are radically changing the Australian environment, for ever. They are displacing native species, altering not only the diversity and interactions of the flora, but also its value for fauna.

 The most obvious change in bushland is when a diverse flowering understorey is replaced by a sward of grasses. Many of our most colourful and interesting animals, including jewel beetles, honeyeaters and the tiny marsupial honey possum, depend on nectar to survive. Grasses are wind pollinated, they produce no nectar. The shrubs that the grasses replaced also had widely differing flowering seasons, so that there was always something in bloom, even in autumn. When grass replaces the shrubs, fewer nectar eaters can survive.

 When Europeans first came to Australia, they found a land full of plants and animals that were vastly different from those they had seen in other continents. Long isolation, poor soils and an erratic climate had led to a rich diversity of unique plant and animal species. The massive granite block (called the Yilgarn craton) that underlies most of the southern part of Western Australia, is one of the oldest land masses on Earth. In the Murchison region, zircon crystals have been found that are 4200 million years old, lying in a conglomerate that was formed 3700 million years ago (Williams and Myers, 1987). This was long before any life began. Mountain ranges have arisen, and then been eroded away, and all this time the south-west of Western Australia has remained as a land surface.

 At one time Australia, together with South America, Africa, Antarctica and India, was part of the great southern continent, Gondwana. Our native plants evolved from ancestors that flourished at that time. Gradually the land mass broke apart, until, about 45 million years ago, Australia finally became a huge island, drifting slowly northwards, currently at a rate of between 6 and 7cm a year.

When Australia first became isolated, the climate was tropical and forests covered the land. Fossils found in the south-west of Western Australia reveal that southern beech, hoop pines, figs, palms and kurrajongs occurred, along with eucalypts and banksias (Wilde and Backhouse, 1977). Gradually the climate became cooler and drier. Every so often, Western Australia became isolated from eastern Australia by oceans or deserts, permitting further specialisation among Western Australian plants. During the last Ice Age, Australia was very dry indeed, and the great sand dune ridges of the central deserts were formed.

 About 140,000 years ago, there was a sudden increase in the number of fires affecting the continent. Was that something to do with the climate, or did it, in fact, mark the time at which Aboriginal people first reached Australia? Certainly, since then, fires have featured in Australian ecology.

Ruby Dock north of Leonora. PH

So, when humans first arrived, they found a continent containing plants and animals that had been evolving in isolation for about 45 million years. To our knowledge, Aboriginal people did not bring any plants into Australia. However, the next big wave of migrants, the Europeans, most certainly did.

 How are plants introduced?

Some plants that are now weeds were deliberately brought here for crops, pastures or as ornamentals. Others arrived accidentally, in animal feed or in the soil around pot plants, for example. Current quarantine regulations are designed to reduce further accidental introductions, while protocols restrict the importation of new species for agriculture and gardens.

 The need for these protocols to be tightened was highlighted recently by a study of pasture plants imported into the Northern Territory (Lonsdale, 1994). Of 463 species imported, only 5 per cent became useful pasture plants, while 13 per cent became classed as weeds. Some of the useful plants were also weedy, so that in fact, less than 1 per cent became useful without causing a weed problem. The cost of controlling the weeds will far outweigh the benefit from grazing the useful species.

The prevention of accidental introductions is the responsibility of every traveller entering Australia.

 Where do plant migrants come from?

There have been plant migrants from all areas of the world, but most of the plants that have been introduced to Western Australia come from Europe or South Africa; however, an increasing number are coming from the Americas and eastern Australia.

Establishment and spread

Once introduced to an area, a plant needs to get established, then it may spread away from the original site. Some species never spread very far from the initial point of establishment, others rapidly spread far and wide.

Sometimes there is a time lag between establishment and spreading from the initial site. The plants that succeed best are the ones that find the right environmental conditions for growth. For example, the Mediterranean climate of the south-west is ideal for plants from similar climates, South Africa, California, Chile and, of course, the Mediterranean itself. The deserts of the world will contribute species to our arid zone, while tropical weeds flourish in the Kimberley.

 The plants that do succeed here are often those which have characteristics that enable them to successfully colonise disturbed ground, and outcompete anything else on site. Soil disturbance could occur due to human operations such as farming, logging, mining, road-making, etc; however, it also occurs after natural events such as cyclones, floods and fires. In addition, many plant migrants have left their predators and pathogens behind, and thus grow more vigorously here than in their country of origin.

Century plant at an old homestead, Yalgoo. PH

Many successful introduced plants have very efficient methods of seed dispersal such as by wind or with the help of animals. For example, on some mid-summer days, city workers often remark that the air in Perth is full of the small parachute seeds of the fleabanes (
Conyza spp.) that grow on building sites. Bridal creeper (Asparagusasparagoides) is being very effectively transported by birds, that eat its fruits, then fly to nearby flowering plants such as one-sided bottlebrush (Calothamnus spp.) to search for nectar. All around these early-summer flowering shrubs, dozens of bridal creeper seedlings arise from the bird droppings. Other plants are being spread principally by human operations such as the movement of weed seeds in grain or on the wheels of vehicles, or the careless dumping of garden waste in bushland.


Some introduced plants, and some native ones too, have become weeds. A weed is a plant growing where it is not wanted. This assumes that a human being has made a decision about whether the plant is wanted or not, and hence it may be accepted at one location but be considered a weed at another. There are no weeds in nature! In this book we have assumed that all introduced plants established outside cultivated areas are weeds.

 What makes a successful weed? Usually these plants are 'disturbance opportunists', they respond positively and rapidly to land or habitat disturbance. Most crop weeds are of this type, since soil preparation for cropping is an extreme form of disturbance. Roadside grading is another operation that creates an ideal weed seedbed. In addition, the grader carries seeds or corms along the road to new locations.

 It follows, then, that disturbed areas around settlements usually show the greatest number of weedy plants. Any form of disturbance such as ploughing, grazing, logging, rubbish dumping or vehicle movements can create ideal sites for weed invasion.

 What problems do weeds cause?

Weeds can be divided into groups, for example, agricultural weeds, bushland weeds and water weeds. A plant can be useful in one situation, but a weed in another, for example, farmers plant lupins (Lupinus spp.), but they are a problem weed in bushland, while goosefoot (Chenopodium pumilio) is a natural part of bushland flora, but an undesirable summer-growing annual in crop paddocks.

 In agriculture, unwanted plants in crops or pasture cost the industry in Australia $4 billion annually. They may reduce yield and contaminate crops, poison stock, reduce stock carrying capacity, downgrade wool or taint milk. Waterways can be choked, shading out native plants and reducing the oxygen available for aquatic animals, and reducing the efficiency of dams and irrigation systems. Home gardeners spend hours of their leisure time keeping weeds at bay. In bushland, introduced plants displace natives, inhibit regeneration, alter fauna resources, affect nutrient cycling, and change the fire characteristics. The result is degradation and eventual simplification of the bushland ecosystem.

Members of the WA Naturalist's Club tackle salvinia in Tomato Swamp, Belmont. PH

 What can you do?

Learn to recognise introduced plants, so that you can be alert for new invaders into an area. It is very much easier to control a problem plant when it is low in numbers and restricted in area. Allowing it to get 'out of control' could lead to major costs in the future. As an example, arum lily (Zantedeschia aethiopica) has spread so widely on Garden Island that the Department of Defence has had to commit millions of dollars to its control.

 Alert the local Shire Council to the presence of a potential problem plant and encourage them to do something about it. Enlist the help of the local community, including schools, it is remarkable what a group of enthusiastic people can achieve. Darlington's 'Wattie Woppers', for example, have almost succeeded in eliminating watsonias (Watsonia spp.) from their suburb. Local parkland may have a 'Friends Group' dedicated to preserving the area, and weed management is usually high on their list of activities.

 In bushland, the best method of weed control is prevention of establishment, which means keeping disturbance of the bush to an absolute minimum. Undisturbed bushland is quite resistant to weed invasion. Disturbance that loosens the soil or adds extra nutrients, for example grazing, off-road driving or rubbish dumping, will encourage weed growth.

 Once weeds have become established, there are four ways in which they can be controlled:

* physical, hand-pulling or mechanical mowing, slashing, cultivating or scalping

* natural suppression, creating a situation where the required plants (native or cultivated) are encouraged to grow and weeds are discouraged

* biological, the introduction of a natural predator or a disease that will destroy the weed without affecting non-target plants

* chemical, the use of herbicides.

 It is not the purpose of this book to give details of control. There are many excellent references which could be consulted, and some are listed in Appendix C.


Declared Plants, legal aspects

Some high priority weeds that are, or may become, a problem to agriculture or the environment can be formally 'declared' under the Agriculture and Related Resources Protection Act, administered by Agriculture Western Australia. When it is declared, a plant is placed in one or more categories according to the control strategies considered appropriate. The declaration may be for the whole of Western Australia or a smaller area. Declared plants are marked with a 'DP' in the text. Landholders with declared plants on their property are obliged to control them at their own expense. Contact Agriculture Western Australia for advice.

 Local Government Authorities are responsible for administering the pest plant provisions of the Agriculture and Related Resources Protection Act. Declaration as a pest plant authorises the Shire Council to enforce control of that plant within its boundaries. Pest plants are marked with a 'PP' in the text.

References (Introduction)

Lonsdale, W. M. (1994). Inviting trouble: introduced pasture species in northern Australia. Australian Journal of Ecology. 19, 345-354.

 Wilde, S. A. and Backhouse, J. (1977). Fossiliferous Tertiary deposits on the Darling Plateau, Western Australia. Annual Report of Western Australian Geological Survey, pp. 49-52.

 Williams, I. R. and Myers, J. S. (1987). Archaean geology of the Mount Narryer region Western Australia. Report 22, Geological Survey of Western Australia. Department of Mines, Perth.


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