Carnivorous plants at Kew

Kew's Tropical Nursery hosts a varied collection of different carnivorous plants from across the world, as Thomas Pickering explains.

By Thomas Pickering

Purple pitcher plant

Behind the scenes in Kew’s Tropical Nursery there is a varied collection of different carnivorous plants from across the world. These plants come from a wide range of different landscapes and climates but all have evolved weird and wonderful adaptations to trap and consume prey. The prey they trap helps to provide the plant with nutrients they would otherwise find hard to obtain in their natural habitats and helps to keep them healthy and strong. 

Cephalotus follicularis 

Some of the most spectacular carnivorous plants in Kew’s collection originate from Australia. Cephalotus follicularis is endemic to a small region in Western Australia. It captures its prey in adapted leaves which form small pitcher traps. These pitchers are highly specialised for insect capture and consumption. The entrance to the pitcher is lined with small downward facing ‘teeth’ which allow the insect prey to climb into the pitcher but make escape very difficult. 

The pitchers are also filled with a solution of digestive enzymes which will break down the body of the prey. The lid of the pitcher, as well as preventing the dilution of the enzyme solution by rainwater, also has transparent windows. The windows allow light to pass through them and it is thought that these help to disorientate the prey trapped inside, reducing any chance of escape. 

Pygmy Drosera 

Another Australasian speciality that we have at Kew is the Pygmy Drosera. These miniature sundews trap their prey in a completely different fashion. The leaf pads are covered in fine tentacles tipped with a drop of sticky mucus. Insects are thought to be attracted to these leaves as they resemble nectar droplets and, on contact, become stuck to the plant as if it were flypaper. 

As they struggle for freedom glandular tentacles become activated by the movement of the bug and slowly but surely bend towards their prey. Once enveloped in sticky slime the insect suffocates and dies. Digestive enzymes released by the plant break down the insect so that its nutrients can be absorbed by the plant. 

Drosera callistos reproduces 

As if these plants were not cool enough already, they also propagate themselves in an interesting way. From November through to January I have been collecting and sowing tiny vegetative bodies known as gemmae. 

Gemmae are actually modified detachable leaves with a vegetative bud, produced in a cup-like structure at the centre of the plant. The gemmae can be so tightly packed together on the plant that they become like a coiled spring. The slightest movement - for example falling raindrops in the wild - fling the gemmae up to a metre from the parent plant. If a gemma lands on favourable ground it will begin to grow and form a new plant genetically identical to the parent it came from. 

Utricularia 

Utricularia is a very widely distributed genus of plants and can be found across the world, from the freshwater fens of the UK to the tropical rain-forests of Brazil. These plants trap their prey beneath the surface of boggy soil or suspended in water, in devices known as bladder traps. 

Utricularia are usually made up of a network of underground or submerged stolons from which shoots grow to form leaves or traps. While waiting for prey, the bladder pumps water out of it forming a lower water pressure inside the trap than out and seals itself with a valve. 

Outside the trap are triggers that, if disturbed by small water borne organisms, open the bladder’s valve. When triggered, water and organism are sucked into the bladder to relieve the pressure difference and the valve snaps shut behind. The entire process happens in about 0.02 seconds, about the average time it takes for a human to blink.

Pinguicula moranensis 

One carnivore appears in many of the zones throughout the Tropical Nursery and is very useful to the horticulturists who work there. Pinguicula moranensis is a species of butterwort native to Mexico and Guatemala. It has large, rounded, glandular leaves which have a slimy surface, and a slimy surface is very sticky if you are a small insect. 

A pest often found in nurseries is a small flying insect known as a sciarid fly. It lays its eggs on the surface of compost and its larvae can cause damage to tender plant material such as seedlings or newly rooted cuttings. The Pinguicula plants act as an indicator to the horticulturist if the sciarid fly population is becoming problematic, as well as helping to keep the population down as much as possible. 

Finding carnivores at Kew 

Many of Kew’s carnivorous plants can be found in the Princess of Wales Conservatory in two rooms dedicated to temperate and tropical carnivorous plants. I started working with the carnivorous collection at Kew about six months ago and I’m hooked. 

Why not visit Kew to get a closer look and check out how ingenious some of these plants really are.