In Pursuit of Australia’s Murderous Flora

Did you know that the Australian continent is the single richest region of carnivorous plant diversity in the world? Let Alastair Robinson, Manager Biodiversity Services at the Royal Botanic Gardens, introduce you to the weird but mostly wonderful world of carnivorous plants, research into which has led him on adventures to some of the most remote habitats on Earth, both to investigate carnivorous plant taxonomy and learn how and why carnivorous plants have evolved, and to discover some of the unusual animals that live in or on these plants.

Carnivorous plants have a disruptive history. When American botanist John Ellis studied the Venus flytrap (Dionaea muscipula) in 1770 and became one of the first people to publicly suggest that some plants may consume insects, his notion was labelled blasphemous and ‘against the order of nature as willed by God’ by none other than Carl Linnaeus, the father of modern taxonomy.

It wasn’t until 1875 that things began to change, when Charles Darwin published his studies of carnivorous plants indicating the theories of John Ellis and other early pioneers of plant carnivory had been correct in their suppositions. Though even he and fellow supporters of the carnivorous plant theory were met with disdain by some contemporaries, the carefully documented and precise nature of Darwin’s experiments made them so reproducible that, by about 1880, plant carnivory was widely accepted as a legitimate concept.

Defined as plants which rely on a variety of ingenious methods to attract and trap prey to obtain nutrients, carnivorous plants are found on every continent except Antarctica across a range of terrestrial biomes. Despite being widespread, they are considered biologically rare. Of the roughly 370,000 species of known flowering plants worldwide, just 800 (or 0.2%) of them are carnivorous, and over a quarter of all of those carnivorous plant species are found only in Australia.

Australia is home to over 230 species of carnivorous plants—representing six of about 18 carnivorous plant genera found worldwide—with a rate of plant carnivory that is four times higher than anywhere else. Their habitats are concentrated mainly in the wettest regions of the continent, particularly the temperate shrublands of southern Australia, where about two-thirds occur in the south-west of Western Australia alone.

Why does Australia have the highest rate of plant carnivory in the world? The answer lies in the soil of this ancient continent. Carnivorous plants evolved globally in response to low soil nutrient levels, their habitats overwhelmingly presenting soils that have invariably been stripped of nutrients by the flow of water, or whose chemistry makes any nutrients present unavailable to plants. These specialised groups of plants eventually evolved to extract nutrients from animals or even animal waste rather than soil, allowing them to compete with other native plants more effectively.

Much of Australia exhibits consistently low soil fertility across a broad range of soil types, but the continent has also been climatically stable for millions of years, with no recent volcanic activity or glacial events, making it the perfect crucible in which carnivorous plant species could evolve and flourish.

These unique plants are, rather surprisingly, hosts to a range of endemic insects, protozoans, fungi and bacteria which depend solely on their association with carnivorous plants for survival. Unfortunately, in the past decades many carnivorous plant species have become critically endangered both in Australia and across the globe as a result of human impacts, be it through habitat destruction, ecological damage caused by agricultural run-off, or the increasingly dry conditions wrought by climate change. As a result of their unusual positions within ecosystems, the loss of even single carnivorous plant species can take whole communities of other organisms with them, making their extinction all the more tragic.

 

Want to learn more? A selection of these weird and wonderful plants, along with many others, are featured on Alastair's Instagram profile.


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