Lots of Lichens

We have a non-plant living on the green roof.  They're very common in Wyoming, but can be quite hidden from first glance.  They look like they could be plants, but they're two entirely different organisms put together.  What are they?  Lichens of course!

Xanthoparmelia chlorochroa, aka tumbleweed shield lichen, is far and away the most abundant lichen in Wyoming. It is unusual in that it is not attached to a substrate (like rock or bark), and it blows about, sometimes accumulating in drifts, especially where vegetation is limited.

Tumbleweed Shield Lichen

In drought years, when plants are not very productive, tumbleweed shield lichen seems really abundant, but likely that’s because it is more visible then. Unfortunately, there have been incidents during drought years when elk have eaten large amounts of the lichen. The organic acids produced by the lichen cause paralysis in elk, so they die of thirst. On the other hand, tumbleweed shield lichen is a favored food of pronghorn, and has long been used as a source of reddish dye and a cure for impetigo by the Navajo.

Lichens are super cool superorganisms! They are really two organisms - a fungus and an alga. Most of what you see is the fungus, but there are photosynthesizing alga cells just below the upper surface.

A cross-section of a lichen

In trade for the moist, sheltered, and nutrient-rich environment that the fungus provides, the alga shares the carbohydrates it makes via photosynthesis with the fungus. Both organisms win! This is a classic example of commensalism, a symbiotic association where both members benefit. And, it is a very successful relationship - there are more than 700 species of lichens in Wyoming, and at least 20,000 worldwide, with new ones discovered all the time.

To paraphrase E. O. Wilson, if you want to discover new species, you should become a lichenologist!

Written by Dorothy Tuthill, UW Biodiversity Institute