Stuck on sundews

August 8, 1997

In the first of a series on young researchers, Julia Hinde goes looking for the origins of Drosera with plant evolutionist Alastair Culham

Those with a passion for plants need not look far for botany's equivalent to the cheetah - an aquatic carnivore too quick to capture on film. Taking just 1/250th of a second to catch a water flea, and with a penchant for small fish and tadpoles, bladderworts are quite at home in streams near you.

Three families and ten species of carnivorous plants inhabit ponds from Hampshire to the Highlands. Some, like the bladderwort, use a powerful mini-Hoover to suck in their prey. Others, such as the sundew family, trap insects in their sticky leaves. Such plants are Reading University botany lecturer Alastair Culham's passion.

As a child, Dr Culham was fascinated by plants, recognising patterns in flora distribution on country walks. Now, at 31, he is a plant evolutionist in charge of a lab and in search of the origins of Drosera, one of the world's most widespread plant families, whose members include the Venus fly trap.

Drosera, or sundews, range from small ground-hugging plants a centimetre in diameter to three-metre-high climbing carnivores, each with familiar sticky leaves and a characteristic flower shape. "There are 180 different sundew species," Culham says, "all with sticky leaves to trap insects. But the growth form they take is very variable."

Unlike most plants, sundews are almost absent from the fossil record. Culham is using their genetic material alongside current distribution patterns in a bid to trace the family's origins. By assuming that plants that are genetically closest have the most similar evolutionary paths, scientists have been tracing Drosera's history. For each gene they have studied so far, Culham says that differences of up to 10 per cent have been found between species of the same family, enabling scientists to identify those most closely related, no matter where they are now found.

Results suggest that the origins of Drosera can be traced back 120 million years to the southern super-continent Gondwanaland, which later split, allowing Drosera to spread around the world. What is now Australia, with more than half the world's species of sundews, was probably their earliest home.

When not on the trail of carnivores, Culham uses DNA sequencing to establish the rarity of plants in a bid to aid species conservation. With colleagues from Kew Gardens, he is trawling through European botanic gardens for samples of endangered species so that breeding programmes can be set up.

"There are at least 30 species in European botanic gardens which no longer grow in the wild," Culham explains. "The cycad, for instance, is a primitive plant related to conifers originating in southern Africa. There is only one left in the wild. It grows side shoots, five of which have taken as individuals, but they are all male and from the original plant. You know with a giant panda that if it stops breeding, it will die out in 30 years, but with trees it's a question of the living dead. Trees can live for about 1,000 years without breeding, but eventually they will die out.

"There is much money from organisations like the World Bank for those wanting to provide new nature reserves, but far less for understanding the biology of rareness and how to preserve species," says Culham. "In the long term, it is an understanding of the biology that will allow us to undertake conservation programmes."

At Reading for seven years, Culham, who rarely travels to where his plant samples originate, but instead receives leaves through the post, leads a nine-strong team, several of whom are older than himself. "I have no problems with the age of those I work with," he says. "People in science are respected for the work they do, not their age."

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