[ INTRO ].

The deep interiors of caves are unique environments. They’re often home to bizarre ecosystems of microbes, fungi, and even animals.

But one type of life you /won’t/ typically see inside caves is /plants/. Because deep underground habitats are missing that one crucial thing all plants crave: sunlight.~ Yet, surprisingly, some plants have found a way around this problem:. They’ve found lights in the darkness—lights that we humans have put there.

These cave-dwelling plants are called lampenflora and their ability to thrive deep underground is amazing… and also a major problem for cave conservation. Caves have preserved a great deal of ancient history, and part of the reason has to do with their unusual environment. On top of the fact that there’s no light deep inside caves, the temperature and humidity also doesn’t change that much.

And in these steady environments, things like cave paintings and ancient artifacts can last thousands of years. It also helps that there isn’t much life there to disturb things. I mean, certain animals can get by if they can rely on senses other than vision.

Like, many bats use echolocation to get to and from their roosts. And there are also cave-dwelling insects and arachnids that have extra-long antennae for feeling their way around. But there generally aren’t plants— because plants absolutely need light.

Not always a lot—for instance, in China there are nettles living in parts of caves where as little as 0.02% of overall sunlight reaches the interior. But you won’t find plants in areas of complete darkness, because they all need some light. And this lack of vegetation is part of why caves make such good natural museums.

The problem is, plants aren’t the only ones that need light. We humans love exploring caves, especially when there’s cool stuff to see, like beautiful cave formations or ancient cave art. Visiting caves is a popular tourist experience, and the tradition goes back hundreds of years.

But we can’t see in the dark. So these days, artificial lighting has been installed in caves all over the globe. And, where there’s light, there can be /lampenflora/.

The word lampenflora was coined in 1963. It’s a German term meaning f lora of the lamps, and it refers to photosynthesizers that grow near artificial light sources in places where they couldn’t naturally live. Most lampenflora are microscopic organisms like cyanobacteria and algae, which can form green mats on cave surfaces.

But these microbes can also be joined by plants like mosses, and in some cases even vascular plants like ferns— although these usually only manage to grow small shoots. The plants that can make it as lampenflora are already well suited to surviving in tough conditions. For instance, lampenflora species include plants that can adapt to low light levels by adjusting the size of their leaves and stems or by boosting their production of chloroplasts, the structures that perform photosynthesis.

Many of them have simple nutritional requirements and can survive in a wide range of ecosystems outside caves too. So, inside caves, mines, and cellars, that little bit of light and heat provided by lamps is all it takes to turn inhospitable darkness into lampenflora haven. As for how plants get inside the caves in the first place—that part’s easy.

Spores, seeds, and cells get carried in by wind, water, and visitors like bats or humans. And once they get started, they can grow into small ecosystems of algae, plants, bacteria, and fungi. The thing is… they don’t really belong there, and while we probably shouldn’t judge them for simply surviving, they can be a serious threat.

For one, lampenflora can be an eyesore, covering up the cave formations and cave paintings that visitors came to see. Even worse, microbes and vegetation often excrete chemical compounds that can damage cave surfaces, destroying formations and paintings that are sometimes thousands of years old. And on top of all that, lampenflora are a source of nutrients, which can lay the foundation for entire invasive ecosystems.

Fungi, animals, and other organisms can come in and even threaten to replace the cave’s unique native inhabitants. This may sound dramatic, but it’s not unheard of for lampenflora outbreaks to get out of control. In the 1960s, Lascaux Cave in France had to be closed to the public in part because of algae growing over its ancient cave art.

And over the years, Lascaux and many other caves have struggled with infestations brought in by visitors and fueled by artificial lighting. So, organizations that maintain these caves, such as national parks, have been working for years to come up with solutions to the lampenflora problem. Treatments like ultraviolet radiation can destroy the flora, but they can also damage cave surfaces and native life.

The same goes for other common treatments like bleach and hydrogen peroxide, or other chemicals. So it’s a hard problem to tackle once it’s gotten out of hand, and that’s why another approach is to address the root of the problem: the light. Many caves are able to hinder lampenflora growth by using dimmer lights, moving the lights farther from cave surfaces, and turning them off when they’re not needed.

Less light means fewer lampenflora. Another surprisingly useful strategy is to change the color of the lights. Because the chlorophylls of most plants work best with blue and red light.

So using yellow or green light can make it harder for plants to grow. Although, this is less effective for microbes like cyanobacteria, which aren’t as picky about colors. For now, the search for the safest and simplest solution for dealing with lampenflora in caves is still a work in progress.

For those of us who love the wonders of the underground, the best thing we can do is keep things nice and dark so plants stay away. Caves might seem mighty and unchanging, but they’re still delicate environments we need to look out for if we want to preserve them. Thanks for watching this episode of SciShow, which was brought to you with the help of our patrons.

If you’d like to help us make videos about cool stuff for everyone, you can go to patreon.com/scishow to learn more. [ outro ].