How to identify a lichen: Part 1

Vulpicida canadensis: A funky neon yellow-green foliose lichen that grows in the forests of the Inland Northwest.

So you’re walking through the forest and you come across an amazing florescent green leafy thing – by golly, you say to yourself, this must be one of them lichen that girl in class is always talking about! Exactly. But how do identify it to species so you can impress that her and get her to go on a date with you? Identify that lichen, figure out its species name. Species names always gets the girls. But how do you figure out what the species of a lichen is? Read on fellow, read on.

Firstly, when you gather any lichen, be sure to note whether that lichen is growing on a rock, on a conifer or hardwood tree, or on a shrub. If it has fallen down from the canopy of a nearby tree it will be laying right dab in the center of your trail – those are my favorites.

Here's the 10x loupe I use for identifying lichen. I find it easier to carry everything I possibly may need on one lanyard around my neck.

Then, you’re going look at some of the macrofeatures of the lichen. If you got a 10x handlens, great, if not, you can still determine the major morphological group. A handlens is ideal for the steps in Part 2, a dissecting microscope for Part 3, and for Part 4 you’ll need a compound microscope with a 100x objective lens if possible, 40x at least.

But if you haven’t gotten your 10x loupe yet, and don’t have access to microscopes yet, you can at least figure out which major morphological group a lichen is, and knowing this is the critical first step towards identifying any lichen.

Parmelia sulcata. Is this Foliose or Fruticose? Hover your mouse over the photograph for the answer. Photo by James Lindsey.

Firstly, hold the lichen in your hand. Look at it. Ponder it. What does the thallus look like? (The thallus is the body of the lichen, and yes, as far as I know every lichen has a thallus.)

Does it have two sides, like a leaf? If yes, then it is a foliose lichen.

Or is it more like the branch of a tree, lacking any really distinction between sides? If yes, then it is a fruticose lichen.

Alectoria sarmentosa; is this foliose or fruticose? (Hover your mouse over it for the answer). Photo by Jason Hollinger.

But what if it is so small that it just looks like paint? Then it’s a crustose lichen.

And what about those ones that have fairy cup like things – what are those? Ah, now thats a tricky question – those lichen have two thalli: the primary thallus is the little tiny leaves that are close to the substrate (those are described as squamulose – a.k.a. tiny foliose) and then there is the secondary thallus which is the fairy cup (podetia) or matchstick (pseudopodetia) or christmas-wreath-like projection (also pseudopodetia).

Cladonia pyxidata: Squamules make up the primary thallus, the secondary thallus is a podetia.

Congratulations! You just figured out the most important distinction between different lichen: foliose, fruticose, crustose, or squamulose. What’s next? Read on to part 2.

Lecanora rupicola, a crustose lichen. Photo by Jason Hollinger.

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