Let me come right out and say it: I love lichens. There.
The reason I love them is the same reason so many people hardly notice them (and when they do it’s usually to pressure-wash them off the patio furniture). They’re often small and unobtrusive, but they’re all around us. Whenever you get up close and personal with a lichen, you enter a completely new world. I didn’t need much encouragement to go lichen spotting in the park for one of my 30 Days Wild.
What is Lichen?
At school I was taught that lichens are a symbiosis between a fungus and an alga. Much later I discovered that although this is broadly true, it’s a bit of an oversimplification. Yes, a lichen always has a fungal element, but it can contain cyanobacteria as well as algae (and sometimes even both).
The extent to which the algae or bacteria and the fungus depend on each other is also debatable. in many cases the fungus seems to get the best part of the bargain, making the algae or bacteria generate nutrients for it through photosynthesis while doing little more than providing shelter. I once read somewhere that a lichen is a fungus which has discovered agriculture, and this is how I tend to think of them.
How Lichens Reproduce
If you stop and think about it for a few minutes, you’ll see that the very nature of a lichen makes reproduction a complicated matter. Lichens reproduce both sexually and asexually, but however they’re to manage it, establishing a new lichen means reproducing the fungus and the algae or bacteria. This being the case, asexual reproduction is less complicated, because the lichen can just bud off a neat little package containing both fungal and algal cells. Sexual reproduction via spores results in a new fungus, which must then partner up with algae or bacteria.
Jam Tarts or Fruit Gums?
One thing I love about sexually reproducing lichens is their fruiting bodies. So far, it’s believed that these can be of four different types (I say believed because lichens are still mysterious in certain ways). On my lichen walk I just discovered one type of fruiting body known as apothecia, although in the interest of fairness I should say that others may have been present but unseen by me. I don’t know all that much about lichens, but I do know that you really need a stereoscopic microscope to get to know them properly.
When I first started using the excellent lichen identification key published by the Field Studies Council, one of the instructions was to see whether the apothecia of the lichen you were looking at resembled jam tarts or fruit gums. Today I found both kinds, as these close-up pictures show (apologies for the less-than-brilliant photos, but I needed to use a high magnification with a small depth of field, and the lichens were on undulating surfaces).
Here’s what the ‘jam tarts’ tend to look like in cross section under a microscope. I made this slide a couple of years ago while studying some lichens from Chile, and it shows the structure really well. The fringe-like things under the brownish layer are sacs containing spores. The round blue shapes below are algal cells contained in a layer within the fungal ‘cup’ (or ‘pastry’, if we’re sticking with the jam tart comparison).
This can be really tricky, because there’s a lot of variation in appearance caused by environmental factors such as the amount of sunshine or pollution the lichen encounters. But, like most difficult tasks, it’s fascinating and rewarding. I’d urge all of you to get hold of a magnifying glass and a set of identification charts and, instead of power-washing the lichens off your walls and patios, to become better acquainted with their complex ways.
To inspire you, here’s a few more of the lichens I found on my walk: