Mosses, Liverworts, and Hornworts (Bryophyta)
Note: this page is an initial sketch. Suggestions are welcome.
Main sources: Encyclopedia Brittanica
Bryophytes are non-vascular plants -- they lack vascular tissues (xylem and phloem) for internal water conduction and support -- thus lack true roots, stems, or leaves -- as well as skin protection (cuticle), and they must therefore depend on their immediate surroundings for necessary moisture. They reproduce sexually by forming male or female reproductive structures, wherein the sperm must swim to the egg in order to form a zygote.
While most mosses (and other Bryophytes) consequently live in wet, shady locations, some have become adapted to alternating wet-active and dry-dormant conditions. Typically land plants, they remain tiny, growing no more than a couple of inches in height. They show their remote ancestry deriving from water plants in that their sperm are motile and rely on water for gamete transport. (They share this and other features with the Green Algae, from which they are thought to have evolved when these Algae invaded the land more than 400 Million years ago.)
Below, an unusually large series of beds of green moss (for our area), located on the strongly-shaded North-facing and steep slopes of a San Manuel Formation cliffside in Lower Hot Springs Canyon and photographed in late February 2004: (Click on the image for a close-up.)
While one might think mosses would be rare in our Arizona Uplands of the Sonoran Desert, we actually find them in quite a number of locations, and in considerable numbers. The key is winter shade (which means fairly steep north-facing slopes) and -- of course -- occasional moisture.
This dark green moss at the left was seen in February 2004 in a protected side-canyon near Jim's Willow Spring (in Cascabel Formation bed-rock). It was in a fairly flat and open space, getting considerable sun, and was somewhat dry, which may have affected its coloring.
Click on the image to enlarge it.
This bright-green moss below was photographed in the Willow Canyon Formation near the Red Trail of Upper Hot Springs Canyon in early March 2004, just after considerable rainfall. The mosses were damp with moisture.
Click on the image to enlarge it.
In another side-canyon of Upper Hot Springs Canyon, also in the Willow Canyon formation, we encountered this gray moss, growing on the north-facing side of this Galiuro Volcanics rock near the Red Trail. Conditions at this time (early March 2004) were quite damp. (Click on the image for a close-up view.)
We photographed these mosses below at the end of December 2004, on the hill above the Old Hunters Camp on Willow Canyon geological Formation where we find the unusual "Sun Ferns" (genus Cheilanthes) shown at the top of the photo. The sun was falling directly on these plants at the time.
These ferns are found here at the base of sharply-angled rock outcrops, which apparently provide considerable additional rainfall runoff to their immediate vicinity. You can see two sets of mosses here more clearly in the close-ups below, with the left-hand image showing reddish, dried-up mosses right below the fern, and the right-hand image showing a group at the lower mid-portion of the above photo: (Click on each image for a close-up view.)...
The lower set on the right appears to have caught considerable moisture from our December rains in this area, and may be actively forming reproductive structures.
We observed another (and even more propitious) location nearby, where two parallel, sharply-inclined planes of Willow Canyon Formation provide a deeply shaded glade in January of 2004, as shown below: (Click on each image to enlarge it.)..
The two pictures are partners -- the one on the left showing the northern-most inclined plane at far left, the right-hand one showing the southernmost plane and the rising staircase of mosses nestled below the top of the channel, where the sun is shining. The runoff channeled into this seasonally-sunless glade has produced a very healty crop of mosses, where you can clearly see the reproductive structures shooting up, below: