by Philip F. May

About this webpage

Here are some suggestions for new students on how to identify leafy, shrubby, or pendant lichens. You will need a key to macrolichens, a glossary, some simple chemicals, and a 10x magnifier (or preferably a dissecting scope). A list of references for the first three of these items may be found in Identifying North American Lichens: A Guide to the Literature

1. COLLECT WISELY. In order to identify lichens, you need good material. Look around for the best available specimen rather than collecting the first one you see. Collect mature thalli, and if possible, fertile ones. Collect healthy specimens, that is, ones without discolored areas. Keep good collecting records: locality, substrate, habitat, elevation, etc. You often need to know where and on what substrate a lichen was growing in order to key it out. (See How to Collect Lichens.)

 2. SELECT ONLY ONE THALLUS TO WORK ON AT A TIME. When you open a packet under the dissecting scope in the lab, you will often find more than one species present. Similar lichen species frequently grow next to each other. Sometimes the lobes completely intertwine. Separate obviously different lichens into separate packets. Now select only one (the best) thallus from one packet to work on, moving the others to one side. This will insure that, if, unknown to you, two species are still present, you'll only be working on one of them.

3. KEEP NOTES. On a 3" x 5" piece of paper, which you will put into the packet, keep notes. Include the characters you decide are present, what key you used, chemical test results, sketches, etc.


5. WHAT COLOR IS THE LICHEN? The hardest decision in keying. Warning: the lichen must be dry. Also, watch out for the effects of lighting. Daylight is best. Cool florescent light is usually fine. Incandescent light can make lichens look yellow. When in doubt, compare the specimen to a lichen of known color. Here are the normal choices:

6. EXAMINE EVERY MILLIMETER OF THE SPECIMEN UNDER THE DISSECTING SCOPE. You are looking for things like isidia, soredia, lobules, pycnidia, apothecia, cilia, whitish spots or ridges, etc. These are often patchily distributed or restricted to a small part of the thallus.

7. IF FOLIOSE, WHAT TYPE OF PHOTOBIONT? Usually it will be a green alga, but not always. It's best to check until you have experience. Very dark lichens often have cyanobacteria, but also some lighter ones. Check a cross-section under the dissecting scope. Cyanobacteria look blackish. If the lichen does have cyanobacteria, IS THE THALLUS STRATIFIED OR NOT? (That is, are the algae confined to a layer just under the surface, or are they distributed throughout the whole thickness of the thallus?)

8. IF FOLIOSE, MEASURE THE LOBE WIDTH. This is an occult art. Many lobes swell or fork at the tips. Measure behind the swollen or forked area. Some thalli have lobes of different sizes. When this happens, you have to guess what the author of the key has in mind. Hale suggests averaging. I usually find it best to use the smallest available well-developed lobes, but sometimes the opposite is needed. Scallops, indentations, and incipient lobes don't count. Generally speaking, "broad" lobes are rounded and "narrow" lobes are linear, but there are plenty of exceptions.

9. IF FOLIOSE, EXAMINE THE UNDERSIDE OF THE THALLUS CAREFULLY. Look for color, presence of a lower cortex (smooth vs. fuzzy), soredia at lobe tips, pores, tomentum (= a dense mat of nearly microscopic hairs), etc. How is the lichen attached? By rhizines or by a central holdfast? If by rhizines, what type? Warning: the underside of lobe tips is often quite different from the underside of the interior. Both are important. Therefore if the lichen is still attached to the substrate, wet a portion of the thallus and fold it back until some of the interior portion of the underside is exposed.

10. IF FRUTICOSE, CHECK A CROSS-SECTION OF THE THALLUS. Is the core hollow? Is the innermost core an elastic thread? Is the area inside the algae more or less uniform?

11. KEY OUT THE SPECIMEN. The most useful key is usually one specifically written for your geographical area. If none is available, then chose a key for a nearby area or use a national key. When using a long key, write down the couplet numbers and choices. If you come to a dead end, back track and try to figure out where you might have gone wrong.

12. CHECK YOUR ANSWER. This is very important. It is very easy to key to the wrong species. Reading a detailed description of a species is helpful in confirming your identification, but it is still quite possible to fool yourself. The best way to check your answer is to compare your specimen to a reliably identified specimen. These are often available in herbaria at certain universities and museums ( Lichen Collections ). Alternately have an experienced lichenologist confirm your work. Once you have confirmed specimens, you can start your own reference collection. I repeat, check your identification against known specimens or send to a lichenologist. This means you! Addresses of lichenologists

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About this web page:

Copyright 1996, 2000 by Philip F. May
Original date online: 01 March 2000
Revised: 13 March 2000
Comments to

Suggested citation: May, P.F. 2000. How to identify a macrolichen {online}. Farlow Herbarium, Harvard University, Cambridge, Massachusetts. Available:

The URL of hyperlinks cited in the text is: