A boulder forms a square column nearly 20 feet tall. Photo by Robert Dryja

A boulder closeup is covered with patches of lichen and moss. Photo by Robert Dryja

By ROBERT DRYJA
Los Alamos

The wooded canyons throughout Los Alamos have boulders scattered in different ways. Large boulders may be standing alone or in piles along a hiking trail. Alternatively, they may be dispersed throughout a broad slope leading into a canyon.

Boulders that are taller than a person are impressive to see, whatever way they may be laying. Something curious also may be seen if they are looked at closely.

Why are some boulders green in color today when they were gray just a few days ago? Why do some have bright orange or red spots? Has someone been painting them?

The answer is with two kinds of life: mosses and lichens. Mosses are a simple kind of plant while lichens are different organisms living together. To confuse matters, mosses and lichens can change colors. Both can be a shade of green one day and of gray another. They also can be living on the same boulder. What is going on?

Plant life began as algae growing in water. Mosses represent the first primitive plant species to live out of water. They do not have the more complex vascular systems for carrying nutrients and water the way more advanced plants do. They also do not have roots for absorbing nutrients from soil. Instead they remain small and absorb moisture through their leaf surfaces.

Although small in height and weight, mosses can compensate in sheer numbers. Sphagnum moss is an example. A single plant may grow up to three inches tall and weigh from 100 to 300 milligrams. A ponderosa tree in contrast may sixty to eighty feet tall and weigh two to three tons. Although any one plant is small, their combined numbers are remarkable. Sphagnum moss is estimated to grow on three percent of the land and water surface of the earth. The mosses here in the Jemez mountains are not as extensive as Sphagnum moss, but still are remarkable in their way.

Mosses can grow on boulders in shady areas. A boulder may look like a gray or brownish colored bare rock. However much of the surface color may be due to moss that turns gray to brown when there has been no rain for a while. The leaves curl up and a state of dormancy occurs when there have been no rains. Moss leaves can be very short and not evident if a boulder is looked at casually. However, the moss quickly turns green when rains arrive. A boulder may look like a large gray rock one day and then green the day after rain.

Mosses grow in the shade of trees towering over them. Rain falling underneath a tree does not evaporate as quickly compared to being in direct sunlight. This helps moss to grow. Moss needs some sunlight for photosynthesis. However, it is adapted to living with a low level of sunlight while gaining the advantage of shaded moisture. This adaptation has another advantage. Mosses do no face competition from plants that require more sunlight.

Lichens grow in the same environment as mosses. A lichen is two or three separate organisms in a mutualistic relationship. Thread-shaped fungi provide a physical support structure for algae or cyanobacteria. In turn the algae or cyanobacteria generate nutrients by photosynthesis for themselves and the fungi. (Cyanobacteria also are called blue green algae.) Lichens can have a variety of colors in addition to a light gray or green. These colors include red, orange, yellow or brown. If the pigments that create these colors are absent, then a lichen may be green to gray in color depending on weather conditions. Like moss, greenish colors appear when a lichen receives rain moisture. It then changes back to grayish colors when dry.

It is therefore easy to confuse mosses and lichens based on color alone, particularly if looking at a boulder from a distance. The physical shape of a moss typically involves a short, slim stem with a spiral of leaves around it. These may be curled up when dry. Lichens in contrast can have a variety of shapes. They often appear like flat, crumpled paper with torn edges. Cones also may present. We may think of plant growth being dense when several trees and bushes are growing close together near a boulder. However, there may be a hundred or more mosses and lichens growing on the boulder but not readily apparent due to their small size and color.

Two other aspects of mosses and lichens are remarkable. Mosses were among the first plants growing out of water. They therefore contributed to oxygen being introduced into earth’s atmosphere and carbon dioxide being reduced. This set the stage for other forms of life to emerge on both the land and sea. Lichens are among the longest living organisms. A lichen species in the arctic was found to be 8,600 years old.

Patches of lichen growing next to one another vary in color from orange to green to gray. Photo by Robert Dryja

The lichen shows both its cone-like shapes and flattened, crumpled paper shapes. A patch of moss is growing on the right side adjacent to the lichen. Photo by Robert Dryja

The leaves of a moss encircle each stem and the stems form a tangled mass. Moisture then can be more readily held among the leaves and stems. Photo by Robert Dryja

A patch of moss with its reproductive stems standing upwards. Photo by Robert Dryja