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Scarred earth meets visitors at the Kirstenbosch National Botanical Garden in Cape Town where some of South Africa's rarest plants once stood. In August, 24 of the park's cycads were stolen, probably to be sold on the black market as landscaping ornaments.

Now, in a last-ditch attempt to save several endangered species from extinction, scientists are turning to forensic methods to see if tracking the history of suspect plants can help to bring illegal traders to book. But time is running out for the plants, which are even more threatened than the country’s emblematic rhinos.

South Africa’s endemic cycads — which look like a cross between a palm and a pineapple tree — rank among the most endangered plants in the world. Of the country’s 38 cycad species, three are already extinct in the wild, and 12 others are critically endangered. Cycads grow slowly, and can live for hundreds of years.

Their striking looks and rarity make them prized collectors’ items, with individual plants able to fetch tens of thousands of US dollars. This profitability is fuelling illegal poaching, even though lawbreakers face up to ten years in prison if caught.

Tagging techniques

Attempts to prevent poaching by various methods have so far failed to stem the loss, especially in the wild. Microchip tags inserted in the plants have been spotted by thieves armed with X-ray machines, and gouged out. A more successful method sprays plants with microdot paint, which deposits tiny identification tags that cannot be seen with the naked eye. However, tagging every plant in a collection — let alone in the wild —is not always feasible.

The new method, developed by scientists at the University of Cape Town and at the South African National Biodiversity Institute in Pretoria, gets around this problem using the plants' own chemistry. It is based on stable-isotope analysis — a common method in forensic science — to track where a plant has lived over its lifetime.

In nature, the relative abundances of a chemical element’s isotopes — which differ in the number of neutrons they have in their nuclei — vary from place to place. As organisms grow, they take building blocks from their environment, making these isotope signatures part of their bodies.

Stable-isotope analysis has helped to identify the origins of smuggled ivory, counterfeit money and drugs. But its suitability for tracking cycads was unknown, which is what UCT plant scientist Adam West and his colleagues wanted to change.

The team sampled two species of cycad: Encephalartos lebomboensis and Encephalartos arenarius. They analysed plants they knew had been relocated and compared their isotope signatures with those of wild plants, and found that it is possible to tell which plants have been moved. Their results, due to be published in the November issue of the Journal of Forensic Sciences1 (see preprint), suggest that the method can track a plant relocation that happened decades ago.

West and his colleagues are currently testing samples from police raids of suspect plants, to see whether their isotopes are consistent with the owner's story or with a wild origin.

He hopes that this might deter illegal dealers. “If you got your cycad from the wild 30 years ago, we can still tell,” he says. The next step is to create a library of wild cycad plants, he adds. This will provide a reference of chemical footprints against which suspect plants can be compared.

Jason Sampson, curator of the Manie van der Schijff Botanical Garden in Pretoria, calls the isotope analysis “an elegant piece of work”. He hopes that it will make a difference to anti-poaching efforts. However, he also says that more needs to be done to sate the demand for rare cycads, by accelerating breeding programmes in captivity.

But West points out that it takes years to propagate cycads, and some species do not have much time left. “In the wild, species are going extinct on the scale of days, weeks or months — not years and decades. We’re losing the battle.”