health & science

Don’t lick sexy pavement lichen - here’s why

It’s called sexy pavement lichen and tonnes are supposedly available for supply but there’s little proof to back up claims it can treat impotence – and plenty to be worried about.

If you see someone on their hands and knees licking lichen on the footpath there’s an explanation.

They’re likely to be after the reported effects of sexy pavement lichen - and be cheap.

There are claims the lichen is a natural Viagra and while scientific evidence of efficacy is scant, there’s a thriving trade in the hardy but slow-growing lichen.

It has joined the of ranks of sea horses, pangolin scales, the penises of tigers and seals as substances rumoured to have an effect on human erectile dysfunction. Trade is legal and thousands of tonnes of ground up lichen are available for purchase on the online Chinese marketplace Alibaba.

However, if you’re after some lead in your pencil, sexy pavement lichen is a literal and dangerous way to get it.

Botanist Dr Peter de Lange, who is partly to blame for the adoption of the lichen’s amusing common name, first heard of the lichen’s reputation from the late Dr David Galloway.

Galloway was surprised to learn the lichen had been ground up, put in capsules and sold purporting to be an ancient Chinese remedy for erectile dysfunction. Galloway gave de Lange a withering view on its therapeutic qualities:

“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.”

The lichen grows on roads and pavements in various parts of the world. It’s so abundant in New Zealand people have complained it causes cars to skid in wet weather. Part of this reason for its abundance is its extraordinary ability to cope with heavy metals. In urban areas sexy pavement lichen contains high levels of copper, lead and zinc.

How did it get the silly name?

If you’re trying to buy sexy pavement lichen online, you’ll have better luck searching it out using its scientific name Xanthoparmelia scabrosa.

With Xanthoparmelia scabrosa being somewhat of a mouthful to say, and with no common name, University of Otago lichenologist Dr Allison Knight, dubbed it “sexy footpath lichen” in a talk given to the Auckland Botanical Society many years ago.

It was a throw-away comment, but she thinks her tongue-in-cheek name must have appealed to someone - possibly de Lange - in the audience.

The name stuck, and now, thanks to de Lange using it as a common name for several lichen images on iNaturalist it's immortalised.

Sexy pavement lichen on the iNaturalist site. Photo: Peter de Lange, iNaturalist, CCO

What’s in sexy pavement lichen

Knight finds the adoption of her joking name amusing but worries about people’s use of the lichen.

“This lichen contains a chemical somewhat analogous to Viagra - and somewhat toxic. I always say in my talks that I don't recommend going out and licking the footpath.”

The lichen has what’s known as a PDE5 inhibitor, this substance inhibits an enzyme which can lead to impotence. However, there’s also a concern it itself could be toxic.

The lichen’s chemistry has been picked up by natural health practitioners and there's an array of products touting Xanthoparmelia scabrosa as a sexual stimulant.

While evidence of efficacy is lacking, claims of the lichen's charms aren't. An advertisement on Alibaba claims its main function is to increase libido, cure sexual and erectile dysfunction. Available in 25kg drums, costs are listed between $92 and $122 a kg. Some suppliers claim they can provide 10 tonnes a month.

There’s every chance what you think you are buying isn’t what you get.

Knight said a United States Food and Drug Administration asked an Australian lichen expert to analyse one of the products. He found it was 80 percent Viagra, and 20 percent grass clippings.

For the lichen, this is probably a good thing.

“Most lichens grow very slowly, just a few mm per year, so it would be scarcely sustainable to harvest them,” said Knight.

She’s perplexed by the quantities on offer on Alibaba. To get 25kg of powder would take a huge amount of lichen and harvesting isn’t easy.

“It’s really quite hard to scrape off the footpath, or anywhere else. Especially trying to scrape it off without getting bits of gritty pebbles and stuff in it.”

Plenty to get excited about

Putting aside the disappointing bedroom performance, and downright dangerous side effects of sexy pavement lichen, there's plenty of fascinating lichen qualities.

For starters they’re not really a single thing but a symbiosis between a fungus and alga or cyanobacterium. The alga or cyanobacterium makes dinner and feeds the fungus, while the fungus provides a cosy, dry home.

The symbiotic pairings have developed incredible mechanisms to cope with harsh environments.

She said that lichens that occur in New Zealand have survived exposure to space.

One experiment reports a lichen sourced from Antarctica surviving after 1.5 years in the vacuum of outer space, where temperatures range from -21.5°C to 59.6°C.

“Between them lichens make over 1000 unique chemicals, mainly for their own protection: sunscreens, antibiotics, antifungals, antibacterials, anti-algal, anti-moss, insect repellents, anti-mollusc, dyeing agents - the list goes on.”

Image from Dr Allison's Knight's free introductory lichen guide showing seven different lichens on one twig. CC BY 4.0

Knight is currently working on a three-part illustrated volume of New Zealand’s lichens to follow-up on her introductory guide. Of the world’s 20,000 described lichens, around 2000 are found in New Zealand. Little is known about half of these lichens.

As long as misinformation doesn't create an army of chisel-wielding toxic lichen gatherers, sexy pavement lichen's future is secure, as is the future of around 643 other lichens. However, 275 of New Zealand's lichens are threatened with, or at risk of, extinction.

Once mostly overlooked, public awareness of lichens is growing, according to Knight. Chances are once people are turned on to noticing sexy pavement lichen, they’ll start to notice other species.