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Tuesday, September 27, 2011

Lookin' for Lichens

Penstemon and lichens in front of the Berry Center.
This is one of our favorite pictures of the Berry Center, because of the Penstemon blooming so prettily in front of the building. But, to the careful observer, the Penstemon is only a minor character in the picture—most of the biodiversity is comprised of lichens. Elegant in their colorful bodies and reproductive structures, and admirable for their tenacity in harsh conditions, lichens are truly unique among living organisms because they are formed through the union of two, very unrelated kinds of organisms. 

What's a Lichen?
Most of what we see in a lichen is the fungus body, which is capable of forming a strong attachment to the substrate and absorbing moisture from rain, fog, or melting snow. Lichen fungi are capable of producing a remarkable array of chemicals, some of which can break down rock (with important ecological implications), give muted or vibrant colors to the lichen, or protect the lichens from herbivory (more on that in a bit). 

But one thing that fungi cannot do, is produce their own food. Like all heterotrophs, fungi must digest organic molecules to get energy and building materials for growth, but they are especially clever at it. Instead of ingesting large particles, then digesting internally, fungi secrete digestive enzymes, then absorb small molecules through their cell membranes. 

Xanthoparmelia chlorochroa nestled among grasses and
forbs in the Laramie Basin.
Which leads to the obvious question: What are they digesting on a rock? These clever fungi are actually keeping their food source inside their bodies—in pockets or layers within the lichen, there are green algae happily (we suppose) photosynthesizing away, and making food for themselves and the fungus. What does the alga get out of the arrangement? A cozy home, attached to the substrate, protected from UV radiation, and more humid that the external environment. 

This arrangement between fungi and algae has been very successful—at least for the fungi. There are approximately 30,000 species of fungi that form lichens, and none of them can be found as free-living fungi. In contrast, only a few hundred kinds of algae (and a few species of cyanobacteria) participate in lichen alliances, and all of them can live on their own, though generally in much more moderate and moist habitats.

Berry Prairie lichen rock.  This rock has eight species
of lichens growing on it
All of this has been a long digression (on a favorite subject of mine), but now it’s time to bring in the Berry Prairie. Are there lichens on the Berry Prairie? Not many, to be sure. In fact, only on a couple of the imported rocks. But lichens are an important component of the native prairie, so we will be watching for them. How will they get here? The commonest of the prairie species is not attached to a substrate at all, so it could blow into the Berry Prairie.

The Black Sheep of the Lichen Family
Xanthoparmelia chlorochroa (aka tumbleweed shield lichen) is called a vagrant, because of it unsettled lifestyle. It can be found all over the Laramie basin, as well as most of the interior west, and is most easy to see where grass cover is low. It’s especially easy to find after a rain, when the body is swollen with moisture. Pronghorn eat lots of X. chlorochroa, especially in the early spring and during drought. Soaking and cooking the lichen in water yields a red dye that is prized among Navajo weavers and other fiber artists. 

Work in progress using yarn dyed with tumbleweed shield lichen.

The bad news is that sheep, cattle and elk can be poisoned if they eat X. chlorochroa. In 2004, several hundred elk died on the Red Rim of the Red Desert (south central Wyoming) after consuming unusually large amounts of the lichen, presumably because of reduced forage due to drought. Scientific investigations have shown that the culprits are acids produced by the lichen, including usnic, salazinic and norsticitic acids. Interestingly, the affected elk had red urine—the same color as the dye made by weavers.

Since we’re not anticipating that sheep, cattle or elk will be grazing on the Berry Prairie, we’re not concerned about any adverse effects of tumbleweed shield lichen. Rather, we look forward to finding it, as an indicator that our artificial prairie is become more like a natural prairie. If X. chlorochroa can get here, so too can many other organisms, and as far as we’re concerned, the more, the better.  

Written by Dorothy Tuthill, Berry Center Associate Director


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