A common species of urban lichen is being promoted as a natural alternative to Viagra, much to the concern of scientists

Botanists in New Zealand are warning the public not to consume lichen growing on footpaths and shady rocks throughout the country, after misleading stories about its stimulatory properties spread rapidly online.

The University of Otago lichenologist Dr Allison Knight dubbed a common species of local lichen “sexy pavement lichen” after discovering it was being promoted as a natural alternative to Viagra in online marketplaces, especially in China.

The fungus’s scientific name is Xanthoparmelia scabrosa, and while it could have some properties that are similar to Viagra, Knight said, it can also be “somewhat toxic”.

Lichen found on footpaths can also be tainted by inner-city pollutants such as dog urine and excrement, car exhaust, arsenic, mercury and lead.

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The lichen in question is a species that only grows in New Zealand and the Pacific, most often in urban areas, and there are hundreds of products selling it in pill and powder form on the Chinese online marketplace Alibaba, retailing for anywhere between US$12-300 per kilogram.

Knight said most of the products available online were made up of 80% Viagra and 20% grass clippings. To her knowledge no rigorous testing had been done of the “sexy pavement” lichen to prove its efficacy or safety for human consumption.

Knight’s tongue-in-cheek name for the species has been adopted by website inaturalist, a popular global scientific initiative by the California Academy of Sciences and the National Geographic Society which describes itself as a place to “identify the plants and animals”.

“It hasn’t ever really been tested, and it is somewhat toxic, so it is not advisable to consume it. But it is a precursor to Viagra, however large quantities could indeed be very harmful” Knight told the Guardian.

New Zealand botanist Dr Peter de Lange also derided the therapeutic qualities of the fungus, telling the Newsroom website that its effect on sexual function could be opposite of what was hoped for.

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But Knight said lichen could have huge health benefits. “It [Xanthoparmelia scabrosa] doesn’t occur all over the world, it doesn’t even occur in China where all these vast quantities are coming from. But lichen does have huge potential, and there is a lot of research underway to see how they can be used for the next generation of antibiotics to replace the ones we are becoming resistant too.”

There are at least 20,000 varieties of lichen known worldwide, 2,000 of which grow in New Zealand, especially on shady footpaths, the trunks of fruit trees and in native forests. Like much of New Zealand’s unique biota, some varieties and species of lichen are now endangered or under threat.

“It is nice to focus people’s attention on lichens, I always say they are hidden in full view,” said Knight.

“They tend to be understudied and underreported. They’re under-recognised, and they’re very important because they are the colonisers – they are the first things that will colonise bare rock. When life came out of the ocean … there was lichen.”