There is scant evidence that it actually boosts libido and sexual performance, and it could be harmful.
Botanists in New Zealand are warning the general public against eating a common lichen that is found growing on urban pavement. This odd behavior stems from a belief that the lichen is a sexual stimulant, similar to Viagra but cheaper. While the 'sexy pavement lichen,' as lichenologist Dr. Allison Knight calls it, does indeed share some properties with Viagra ("a PDE5 inhibitor, which may inhibit an enzyme responsible for impotence", via Wikipedia), it also offers up a host of other nasty ingredients.
Because it feeds on pavement, this particular lichen, Xanthoparmelia scabrosa, is rich in heavy metals. To quote Dr. David Galloway, "About the only thing that people would get from using that is a healthy dose of cadmium, arsenic, mercury and lead. Basically, anything that you would find in asphalt, roadsides, pavements. So, it would actually do the exact opposite."Despite this, there is a thriving black market for the lichen, currently available on the online Chinese marketplace Alibaba. where it promises to "increase libido, cure sexual and erectile dysfunction." Newsroom reports that, when the U.S. Food and Drug Administration asked an Australian lichen expert to analyze one of these Chinese-sourced products, it was found to be 80 percent Viagra and 20 percent grass clippings – hardly the natural stimulant buyers hope it to be.
Dr. Knight says she is confused by the quantities offered on Alibaba, with suppliers selling 25-kg drums that cost up to NZD$122 (US$78) per kilo. "Most lichens grow very slowly, just a few [millimeters] per year, so it would be scarcely sustainable to harvest them." She points out that they're also difficult to harvest: "It’s really quite hard to scrape off the footpath, or anywhere else... without getting bits of gritty pebbles and stuff in it."
So, in case you were considering it, sexy pavement lichen is not the way to go for boosting intimacy, but Dr. Knight doesn't want to discourage people from getting excited about lichens. They are incredible plants with great potential for other medicinal needs, such as developing new antibiotics to replace ones we've become resistant to. And they are the original colonizers, one of the most ancient and resilient forms of life, worthy of our admiration. In Knight's words, "When life came out of the ocean... there was lichen."