Carnivorous plants: studying the meat-eaters of the plant world

Australia is home to more carnivorous plants than anywhere else in the world, with approximately 250 species of these evolutionary wonders endemic to the continent.

Our low-nutrient soils, having gone relatively undisturbed for millions of years, have provided the perfect conditions for these predatory plants to evolve and adapt to their environment.

Recently, Curtin University PHD candidate and botanist Thilo Krueger, and his academic co-supervisor Dr Andreas Fleischmann, travelled to Australian Wildlife Conservancy’s (AWC) Charnley River–Artesian Range Wildlife Sanctuary in the remote Kimberley to study these fascinating plants. Here they discovered multiple undescribed species of sundew and bladderwort, along with a new and unexplored site aptly named ‘Sundew Spring’!

New discoveries at Charnley River–Artesian Range Wildlife Sanctuary

Tom Sayers/AWC

‘Charnley River has an amazing number of different habitat types,’ explains Thilo. ‘There are so many species of carnivorous plants, and each species tends to inhabit a specific kind of habitat. One species may only occur in swampy environments, another in sandy soils that are relatively dry, and some species only occur in sandstone seepage areas where there’s just a little bit of water trickling over the sandstone rock. And Charnley River has all these and more.’

This diversity of habitat might explain why there are so many species at Charnley River–Artesian Range Wildlife Sanctuary. Thilo believes the sanctuary protects one of the highest concentrations of carnivorous plants in the Kimberley.

One area, named ‘Sundew Spring’ by AWC Wildlife Ecologist Dr Tom Sayers, shows just how prolific the region is for carnivorous plants.

Andreas Fleischmann/Botanische Staatssammlung München

‘Having spent a few days in the field with Thilo and Andreas, their enthusiasm for carnivorous plants was infectious, and I was keen to locate more substantial populations,’ says Tom. ‘Carnivorous plants can be particularly abundant in spring-fed sandseep environments and so I took to satellite imagery. One region on the Synnot Range looked very interesting and so I ventured out there. On arrival I was astonished at the scale of the carnivorous plant populations and on return contacted Thilo and Andreas who had since moved on to another field site in the Kimberley. Given the scale of the population and the presence of undescribed species, they returned to Charnley to study the population at ‘Sundew Spring’.

With Charnley being a hotspot for carnivorous plants, and myself having a background in plant-insect interactions, we at AWC plan to opportunistically map carnivorous plant habitat on sanctuary to help external researchers uncover the mysteries of these fascinating plants.’

Thilo Krueger/Curtin University

It’s a very fitting name for a site that is, quite literally, a field of millions of sundews – each dripping with a sticky substance that attracts and traps prey. Globally, sundews come in all different shapes and sizes, from some of the smallest plants in the plant kingdom to tall climbers and individuals more than a metre in length.

Multiple undescribed species of sundew and bladderwort were found during the visit and Thilo and Andreas hope to return to the area during the wet season to find and study additional species.

So, what are carnivorous plants?

Tom Sayers/AWC

Carnivorous plants use a variety of strategies to lure prey into their traps – from strong-smelling nectar to vivid colouration that mimics flowers. All for the valuable nutrients they contain.

‘Most carnivorous plants are found in very nutrient-poor soils that are deprived of nitrogen and phosphorus. Because of this there’s this evolutionary pressure for the plant to evolve alternative strategies,’ explains Thilo. ‘If there’s not enough nitrogen or phosphorous in the soil, the plants need to get these elements from somewhere else, for example, by carnivory.’

Carnivory has evolved repeatedly over the 140 million-plus years that flowering plants have been in existence and occurs in unrelated plant families. Each time, the driving force has been the same: the need to find an alternative source of vital nutrients.

Carnivorous plants use leaves adapted to act as traps. They also have flowers for pollination that are often found at the end of long stalks – kept separate from the traps.

How can you tell what carnivorous plants eat?

Tom Sayers/AWC

‘Some researchers have suggested that there may be a conflict for carnivorous plants, as they rely on insects for prey and for pollination. While one could assume that they are wind pollinated to avoid this conflict like some other flowers, interestingly, all carnivorous plants are insect pollinated – and don’t want to catch their own pollinators,’ says Thilo. ‘So, one of the specific things my project will be researching is if there is an overlap in the prey and pollinator spectra of these plants.’

Thilo is doing this by utilising a new method called DNA metabarcoding. This method involves collecting a sample that includes the DNA of everything associated with the plant – the plant itself, prey and all the insects that have been on the leaves or flowers as well.

When an insect pollinates a flower, it will leave behind tiny amounts of DNA in the shape of scales, hairs, or excrement. By collecting the whole leaf or flower Thilo is able to compare all the DNA present with a DNA library of known species and prey species sequenced by other researchers. This allows him to identify the animals that have been captured and in contact with the plant.

Disappearing curiosities

Tom Sayers/AWC

There is still so much to learn about these oddities of the plant world.

‘The amazing thing is how easy it is just to stumble upon new species in the Kimberley,’ says Thilo. ‘Almost every time I travel there, I find something I’ve never seen before, just waiting for someone to describe it. In fact, the rate of discovery of new species is so high that it’s almost impossible to catch up and describe all of them!’

However, as fast as we are discovering them, we also face losing them. In a paper Thilo and his supervisors published in 2020, it was found that more than a quarter of the world’s carnivorous plant species are threatened with extinction. In fact, as well as having the highest number of species, Australia has the highest number of threatened species of carnivorous plants in the world.

Habitat loss has historically been the main driver of the disappearance of populations and species. Now, especially in south-west Western Australia, the changing climate presents a significant threat to these plants that often occur in wetland areas and are very sensitive to heat and dry conditions.

The following images were all taken by Dr Tom Sayers/AWC.