Lichens That Grow on Stone

Since I recently did a post about lichens that grow on trees I thought I’d do one on lichens that grow on stone. Though there are lichens that can grow on wood or stone most of the ones I know seem to prefer one or the other. In fact the ones I know seem very fussy about where they grow, even down to the species of tree or stone. The lichen in this first photo is not that fussy though, so it will even grow on sidewalks, and that’s how the name sidewalk firedot lichen (Caloplaca feracissima) came about. Though I’ve seen it on concrete once or twice in the past I almost always see it on lime rich stones. It’s a pretty orange color and it can get quite big. This one is as big as a car tire.

Another lichen that can get quite big is the peppered rock shield lichen (Xanthoparmelia conspersa) but this example must have just gotten started because it was quite small and had few apothecia. This lichen likes to grow on stone in full sun and I find a lot of them on stone walls. They’re a good introduction to lichen study because their brown apothecia, where their spores are produced, are large and easy to see without aid.

Lichens are made up of a symbiotic relationship between fungi and algae or cyanobacteria. Technically apothecia are “fungal reproductive structures, in which the fungus reproduces itself through the production of spores” This is not the only way that lichens reproduce, but it is common and the apothecia are often beautiful and well worth watching for. The beautiful brown ones in the photo above belong to the peppered rock shield.

Some lichens are very easy to identify because there aren’t many others that look like them, and the toadskin lichen (Lasallia papulosa) is one of those. Toadskin lichens show color changes when they dry out like many other lichens. When wet it is pliable and pea green and when dry it becomes crisp and ash gray like the above example. Toadskin lichens get their common name from their many “warts.” They attach themselves to stone at a single point that looks like a belly button, and that makes them umbilicate lichens.

This is the very same toadskin lichen as the one in the previous photo. You can easily see the dramatic color change between this day when it was wet and when it was dry in the previous shot.

Rock tripe lichen (Umbilicaria mammulata) is a relative of the toadskin lichen but it doesn’t turn gray when it dries out. Instead it gets brownish and curls up. It is very pliable and rubbery when it’s moist, but once it dries out it becomes crisp like a potato chip. The Umbilicaria part of the scientific name comes from the Latin umbilicus, meaning navel. This is where another common name, navel lichen, comes from and points to how, like the toadskin lichens, they attach themselves to stone with a single attachment point that looks like a navel. It sticks itself to stone by way of this single, navel like attachment point and the rest of the lichen hangs from this central point, much like a rag hanging from a peg.

Here is what rock tripe lichens look like dry. You can see the back of it, which is black and pebble textured. Rock tripe is edible and eating it has saved the lives of people who were lost and starving in the past. Though I imagine they must taste like old rubber, these lichens were a source of emergency food for Native Americans and saved the lives of many an early settler. Even George Washington’s troops are said to have eaten rock tripe to survive the brutal winter at Valley Forge in 1777.

Rock greenshield lichens (Flavoparmelia baltimorensis.) Look like melted candle wax to me. They are very common in this area and are another of those bits of nature that you see so often they no longer register, but when you take the time to look closer you find that they are quite pretty.

If you happen to see a stone that looks like it has sprouted gray hairs you might want to take a closer look, because there’s a good chance you’re seeing a Cladonia lichen.

There are many Cladonia lichens including the well-known pixie cups, but I think these were peg lichens (Cladonia sobolescens.) Peg lichens are also a large group, with split pegs, thatched pegs, powdery pegs, etc., but these seem to fit the description of what the book Lichens of North America calls simply peg lichens. The “peg” is called a podetium and it is topped by brown apothecia.

Here is a closer look at the tiny tan / brown apothecia that sit atop the pegs. These are where the lichen’s spores are produced. They are so small that I wasn’t able to see them but luckily the camera could.

This peg lichen is a squamulose lichen, which means it is scaly, but it is also foliose, or leafy. Squamules are the small leafy, lobed growths that are at the base of the tiny peg shaped podetia. A podetium is an upright secondary thallus in Cladonia lichens. It is a hollow stalk extending from the primary thallus. Podetia can be pointed, club like, cupped, or branched in shape and may or may not contain the ascocarp, which is the fruiting body of the lichen. If the asocarp is bowl shaped it is an apothecium. In this peg lichen the podetia are not branched and the leafy squamules are rounded and grayish green to brown, with white undersides. The quality of these photos isn’t great but the various parts of this lichen are very small. I think they do show enough to make a fairly good identification but if I’m wrong I hope someone will let me know.

Scattered rock posy lichens (Rhizoplaca subdiscrepans) can be quite small and difficult to see without magnification, but it’s worth looking for them because they almost always have their bright orange apothecia showing. They like to grow on stone, especially granite, in full sun. They don’t seem to change their color when they dry out like many other lichens do. I’ve seen this pretty lichen even on mountain tops.

Here is a closer look at those pretty rock posy apothecia. The ones I’ve seen are never shiny. They always have a kind of matte finish.

Common goldspeck lichens (Candelariella vitellina) are uncommonly beautiful. Look for this bright yellow crustose lichen on stone. especially slate. I see it on older gravestones quite often. It shouldn’t come as a great surprise that, at high magnification, the body of the common goldspeck lichen looks like it’s made up of tiny golden specks. The book Lichens of North America describes the body of this lichen as “little cushions of flattened granules.” This lichen is sometimes sterile, with no fruiting bodies present, but this one had a few. Crustose lichens form crusts that tightly adhere to the substrate that they grow on and usually can’t be removed without damaging it.

The golden moonglow lichens (Dimelaena oreina) that I see are usually about an inch across but they can get much bigger. They grow in full sun on granite and don’t seem to change color when they dry out like many other lichens do. The one in the photo was producing spores and that’s something I don’t see this lichen do very often. If you spend much time in cemeteries you have probably seen this pretty lichen, because it seems to like growing on smooth, polished stone, especially granite. It is a crustose lichen, so removing it from a gravestone would be a challenge. When lichens grow on glass the acids in them can actually etch the glass and this is a problem in the big European cathedrals, especially. I would think the same would be true for polished stone.

Another lichen common to stone walls is the sulfur dust lichen (Chrysothrix chlorina.) It’s a very soft, pale yellow and hides under overhangs so it doesn’t get rained on. At least I think that’s why I always find it tucked away like this, but this is odd behavior for a lichen because they usually like a lot of rain and sunshine.

Dog lichens (Peltigera) are good example of lichens that will grow on soil, rotting wood, or stone as this one was. Dog lichens are associated with mossy areas because the mosses help provide the moisture that they need. It is very thin and pliable. It is also a foliose lichen because it is lobed, or leaf like. The upper part of the body (Thallus) is undulating or veined on this example. This lichen is large and easy to see. It is also probably quite old.

Here is another look at the dog lichen. They’re much bigger than most other lichens. I’d guess this one is about the size of a 45 RPM record, if anyone can remember those.

The underside of a dog lichen is often bright white as this one was. They also have small hairs called rhizines which help them cling to whatever they’re growing on.

Smokey eye boulder lichen is a favorite lichen of mine. The blue color seen in the above photo is caused by the way light reflects off a waxy coating on the fruiting bodies, which is very similar to the “bloom” found on plums, blueberries, and grapes. In addition to blue it can also appear black or gray depending on which direction the light happens to be coming from.  The greenish-gold background color is the color of the body (thallus) of this crustose lichen. It’s a very beautiful thing and I hope you’ll take the time to look for it and all of the other beautiful lichens out there.

There is no absolute scale of size in nature, and the small may be as important, or more so than the great. ~Oliver Heaviside

Thanks for coming by.