Question Answered by Kristin Kaser, Plant Ecologist, INL ESER Program
Southeastern Idaho is part of the Great Basin Desert, the largest desert in North America. It is classified as a cold temperate semidesert steppe with hot, dry summers and cold, snowy winters. During temperature extremes, some of our animals migrate to find needed food and water. Plants, however, cannot move. How do they survive then? Plants have had to come up with alternative ways to cope with hot and cold temperatures and periods of drought.
Lichens and mosses may confront extreme drought by drifting into a dormant state in which they can stand losing over 95% of the water content, returning to full activity upon rehydration. These so-called “resurrection plants” are able to survive in very hard conditions.
Other plants can withstand water deprivation to some extent by closing their stomata (pore openings in the stem or leaf), but if water loss exceeds 40%, the cells are damaged and the plant eventually succumbs to death.
However, resurrection plants are a group of plants that can dry out, go dormant, and rehydrate. Some of them are lichens, some are mosses, and some are spikemosses like the Rose of Jericho (Selaginella lepidophylla) shown below.
Lichen and Moss
Lichen and moss are commonly confused. After all, they are both small things that grow in shaded places and resemble neither a mushroom nor a vascular plant. They are both also cryptogams, meaning they reproduce without seeds or flowers. Sometimes, the term “moss” is often applied to lichens.
So, what’s the difference? In short, a moss is a simple plant, and a lichen is a fungi-algae sandwich.
Mosses are multicellular organisms with leaflets containing chlorophyll to perform photosynthesis, just as vascular plants that include trees, ferns and wildflowers.
But unlike these vascular plants, mosses don’t have specialized tissues that actively transport water and nutrients from the ground to the leaf tips, and vice-versa.
Instead, like a leafy, green sponge, mosses simply absorb water and nutrients. This means they can’t grow too tall or they risk drying out at the top.
Lichens are a mix of at least two different organisms, a fungus and alga, living together as one.
In the simplest case, a fungus surrounds a colony of algae. The algal cells provide food for the fungus via photosynthesis, while the fungal partner protects the algae from drying out and sun damage.
When wet, the algae become visible through the top fungal layer, giving the lichen a green color that can resemble moss. But when dry, lichens are rarely green, and instead come in many vibrant colors. Lichens also have diverse growth forms, but lack leaves of any kind, which helps to tell them apart from mosses.
Remember: Freddy Fungus & Alice Alga took a Lichen to each other!
Materials: Magnifying glass
- Find some lichen. In southeastern Idaho, lichen can be found in many places: tree bark, lava rocks, walls, gravestones, roofs, and even in the soil as part of a biological soil crust. They can be green, red, orange, yellow, blue, black or white.
- Use the magnifying glass to look closely at the lichen. Can you see different types? Are all the patches the same size? Are the lichen patches on the same substrate (base material)?