It's December and that means it's cold up here in the north. There aren't many fungi around to choose for fungus of the month. But this month's fungus was so easy to come up with it's a wonder I didn't pick it previously. Santa's reindeer have to eat something....

An important phenomenon here in the north is that many plants die back, and many perennial plants lose at least their leaves. This is important in terms of ecology, since herbivorous animals are left with far fewer meal choices. In Wisconsin the animals are forced to start eating small twigs- and apparently any plant they can find in my yard... In the FAR north, where they're aren't any trees (i.e. past the tree line), animals have to find something else to eat, and for much of the year the reindeer (called caribou in North America) subsist on the carpets of reindeer lichens that cover the ground in the tundra. According to what I've read, the reindeer still have to dig down under the snow to eat these lichens. Often there are significant battles over the use of a particular bed of lichens (the origin of the term "reindeer games" ???). Reindeer may also get frisky from eating hallucinogenic Amanita muscaria.

In common usage this is sometimes called reindeer moss, but of course it's not a moss at all. Moss is one of many overused terms in botanical common names. The true mosses (Bryophytes) have a dominant gametophyte and no vascular tissue or seeds. Club mosses are lower vascular plants in the phylum Lycophyta. Spanish moss is actually a flowering plant, a member of the pineapple family! So you can easily see why I prefer to use the name "reindeer lichen" for the fungus of the month rather than reindeer moss.

There are actually several dozen species that are called by the common name reindeer lichen. I've only picked one of them, and the species pictured may not actually be Cladonia rangifera. Systematics of this group is very difficult. Some researchers actually place the reindeer lichens in another genus, Cladina, but the vote is still out as to whether there are two or more genera masquerading under the single genus Cladonia.

As you may know, a lichen is a "dual organism," a mutualistic association between a fungus (the mycobiont) and an alga or cyanobacterium (the photobiont). Usually neither can survive on its own. Note that I've used the term "mutualism" here, although this association is often referred to as a symbiosis. Symbiosis is a less specific term that just means "living together," and in modern usage it can refer to either a parasitic or mutualistic relationship. In a parasitic relationship one organism benefits and one is harmed. In a mutualism, both organisms benefit.

Lichens can grow in very inhospitable environments-- on rocks, sides and branches of trees, gravestones. However, lichens are very sensitive to air pollution, especially sulfur and nitrogen, and so they are natural indicators of air quality. Lichens grow extremely slowly, usually 1-2 mm per year. Lichens are important in the environment because they break down rocks into soil, and they help to stabilize soil that's already there.

Ordinarily the fungus is the dominant member of the mutualism. The fungus controls the morphological form i.e. lichens formed with the same fungal species, but with a different algal species may have the same form. Although the alga occasionally determines the form, lichen systematics is essentially fungal systematics.

The Mycobiont: The fungal mutualist may belong to one of over 500 genera and over 13,500 species of lichen-forming fungi ---about 20% of known fungal species Although a few are Basidiomycota (about 20 species) or deuteromycetes, most are Ascomycota, coming from 16 orders, 5 of which are entirely composed of lichen-forming fungi. Lichenized and non-lichenized fungi may occur in the same order. Taxonomically, the lichenized fungi are widely distributed in the Ascomycota. It is not known whether the fungal partners have an extensive independent existence in nature.

The Photobiont: At least 26 genera are members of the lichen association, including 8 cyanobacteria and 1 yellow-green alga. Nostoc is most common cyanobacterium and is able to fix nitrogen when part of a lichen. Trebouxia , a green alga, is found in 75% of lichens in the temperate zones. All the photobionts are probably able to exist independently in nature, although they are not often found this way.

What do the partners get out of the association? The fungus gains nutritionally from the photobiont including sugars from photosynthesis, vitamins, and nitrogenous compounds. Over 90% of the carbon fixed photosynthetically is passed to the fungus. According to Vernon Amadjian of Clark University, it is more difficult to assess the possible advantage for the photobiont. Although the alga may be able to inhabit new environments because of this association, it sacrifices its ability to grow and reproduce at its maximum rate and does not appear to be dependent on this association for its welfare.

Lichens may take one of three basic morphological (growth) forms

• Crustose-- flat and crusty, not easily pried from the substrate [C, Graphis scriptis]
• Foliose-- leafy, but usually prostrate on the substrate. Usually it can be pried off the substrate more easily than crustose forms. [A (Lobaria pulmonaria) and D (anyone know? it's from Maine)]
• Fruticose-- usually upright or hanging, often with bright color somewhere [B, British soldier lichens]

Lichens usually reach maturity and produce ascocarps at 4-8 years of age, The age of some lichens in alpine-arctic area is 1000-4500 years. Their longevity can be partially attributed to their ability to survive long periods of drought unharmed.

So after learning all this about lichens (quiz: which morphological form is the reindeer lichen?), you are free to imagine the reindeer fighting for their lichens on the tundra. One problem with reindeer being forced to survive on lichens is that lichens are very sensitive to pollution in the air. As environments become more polluted with sulfur dioxide and heavy metals, lichens die and the food source for these animals can become limited. Another problem is that lichens accumulate radioactivity, especially strontium (⁹⁰Sr) and cesium (¹³⁷Cs). One of the first indications that there had been a nuclear accident in 1986 at Chernobyl (then in the Soviet Union, now in the Ukraine) was that the lichens were absorbing nuclear fallout and this was accumulating in the milk and meat of the reindeer. Thousands of reindeer had to be destroyed in Scandinavia

Besides being a food source for caribou/reindeer on the tundra. Lichens have the following human uses:

• The manna referred to in the bible was probably the lichen Lecanora esculenta, a lichen that grows in the mountains around Israel and may be blown loose into the lowlands
• Lichens are the source of many natural dyes, including classic tweed.
• In less enlightened times, one lichen (Letharia vulpina) was used by the *pioneers* as a wolf killer. The lichen was stuffed into dead chickens and left out for wolves to consume. After the chicken was digested in the guts of the wolf, the lichens released usnic acid, which in crystalline form cut up the insides of the wolf's guts, so that the wolf would bleed to death internally.
• The chemical in litmus paper (which indicates acid or base) is made from a lichen

Another great site is LichenLand from Oregon State University. A very user-friendly page about lichen biology, with many pictures and a synoptic key to Northwest Lichens.

You should also visit the Wisconsin Lichen page at http://www.botany.wisc.edu/wislichens/ for some very interesting work. A very nice site!

Also be sure to look at some seasonal Christmas Fungi-- check out my popular updated page:
Fungi that are necessary for a merry Christmas

I hope you have a Merry Christmas!

Return to Tom Volk's Fungus of the month pages listing