…from Nature Forward’s introductory class in lichens of Maryland, taught by Natalie Howe, in the NHFS program. (Without the goofy puns.)
1. Most naturalists understand a lichen to be a symbiosis between a fungus and a photosynthetic organism, either an alga or a cyanobacterium. The fungus provides water and protection for the photosymbiont. Typically, in a structure called a thallus, the photosymbiont is sandwiched between layers of the fungus (the mycobiont)—sort of like a lasagna. In turn, the fungus receives sugars produced by the cyanobacterium or alga.
But the association may be much more complex, with other types of organisms participating. These can include secondary algae, non-photosynthetic bacteria, yeasts, protists, and viruses. On the lichen’s surface, the role of microinvertebrates like tardigrades and nematodes is being explored.
So, what is a fungus? Your answer might depend on whether you see the duck or the rabbit. Trevor Goward, in a brief paper in Evansia, writes,
Next time you pause to contemplate a lichen, consider the strong likelihood that whatever it is you see staring back at you – fungus, alga, thallus, parasitism, mutualism, agriculture, gall, growth chamber, or farmstead – in some way reflects the particular mindset you bring to it; that what you’re looking at is really a face in the mirror; and that the face in the mirror is very much your own.
2. In many cases, you’ll have to be content with an identification to genus, especially in the field. The identification keys often depend on
- testing the chemistry of the lichen, either with reagents like KOH and phenylenediamine,
- examining spores with a microscope,
- or performing TLC (thin-layer chromatography) back in the lab.
Just to make things more complicated, the bushy “reindeer lichens” that you may have seen growing on soil, formerly in the genus Cladina, are now in the very diverse genus Cladonia, which includes various organisms named pixie cup, British soldiers, and powderhorn lichens. Cladonia gets its own key in the guides.
All that said, you can usually make an ID limited to a group of a few species, and often use geography and habitat to reduce your choices even more.
Even if you don’t intend to make a field ID, break out your hand lens (you did bring your hand lens, right?) to examine the tiny cilia on a Parmotrema ruffle lichen, the minute lobes of Candleflame Lichen (Candelaria concolor), and the wee horns of Cladonia ochrochlora.
3. Studying lichens in the field is great if you like buying new gear, like a macro lens for your SLR, or a flashlight that throws ultraviolet light. Lichens in the genus Pyxine are drab gray in visible light, but they light up in brilliant yellow under UV. Somewhat like green plants that show red in their basal rosettes, lichens that reflect UV light do so to avoid being scorched by too much light.
4. With your eye this close to the substrate, you’ll meet lichen-adjacent organisms. Mosses growing on soil can provide a moist microhabitat for lichens; myxomycetes are doing their own thing; liverworts like Frullania sp. growing on tree bark might fool you; certain fungi are lichen parasites; and then there are ordinary “non-lichenized” fungi doing what they usually do, decomposing.
5. Natalie describes the lichen community as the “quiet Lorax.” Despite what we know about many lichen species’ sensitivity to air pollution (SO2, NH3, NOx, and O3), only two species are listed under the Endangered Species Act (Cetradonia linearis and Cladonia perforata). Perhaps more surprising, no non-lichenized fungi are listed. The United States does not maintain a nationwide Red List for fungi.
