Alabama is home to more than 400 species of bryophyte, more commonly known as mosses, liverworts, and hornworts. With so many species (there are 20,000 globally), bryophytes do more than provide the greenery that softens rocky streams and wooded landscapes; they are also home to many microorganisms and are an integral part of Alabama ecosystems. Bryophytes are generally small and unfamiliar as individual species to most people, so it can be difficult for the general public to separate them out from other mossy-looking growths.
Bryophytes belong to the plant kingdom and differ from other plants in that they are nonvascular. Nonvascular plants do not have the tube-shaped vascular structures that provide support and rapid transport of water and nutrients found in the vascular plants, which include ferns and seed-bearing plants. Not all nonvascular plants are bryophytes, however, as the term also applies to botanical organisms that are not plants, such as lichens, fungi, and many types of algae. Like other plants, bryophytes produce an embryo as part of their reproductive cycle. The embryo develops from a fertilized egg and is an immature plant held and nourished within the body of the maternal plant. In flowering plants and conifers, the embryo lies within the seed. In ferns and bryophytes, the embryo is held within the archegonium (egg-producing structure). Fungi and algae never produce embryos. Thus, it is important to note that not all small and mossy plantlike organisms are bryophytes, even when they are called mosses. For example, Spanish moss, most commonly seen draping trees in the lower Southeast, is a flowering plant, and reindeer moss is actually a lichen.
There are three distinct groups of bryophytes: mosses, liverworts, and hornworts. These groups are distinguished on the basis of leaf arrangement, the form of the plant body (some liverworts and all hornworts lack stems and leaves), and details of the spore-producing structure (known as the sporangium). Bryophytes occur throughout Alabama. Most are terrestrial, growing on tree trunks, logs, rocks, and soil. They are abundant in moist areas, but only a few are truly aquatic, such as the water mosses (Fontinalis species) and the moss Fissidens fontanus. Given their small size, bryophytes native to drier areas often escape notice, but they are present on most trees in Alabama and in most lawns. Many also occur in cracks and crevices in asphalt, on the face of concrete walls and on rooftops. In the humid woods of south Alabama, several liverworts that are common in the tropics grow on the upper leaf surface of evergreen trees and shrubs, especially leaves of southern magnolia (Magnolia grandiflora).
The greatest abundance and diversity of bryophytes is found in the Cumberland Plateau physiographic section in northern Alabama. The area's forested slopes, rocky ravines, sandstone canyons, and limestone outcrops offer varied microhabitats that differ in terms of exposure to sunlight, drying winds, and the chemical makeup of the soils, rocks, or trees that the plants grow upon. These microhabitats support diverse types of bryophytes, many having specific habitat requirements. The dwarf four-toothed cave moss (Tetrodontium brownianum), for example, is found in Alabama only on rock within the shady recesses of sandstone bluff shelters. The mosses Hyophila involuta and Platydictya confervoides grow on limestones and other calcite-based rocks, and the sharpleaf hookeria moss (Hookeria acutifolia) prefers deeply shaded, moist recesses of rocky cliffs and small streams. Species such as Drummond moss (Drummondia prorepens) and the liverwort Leucolejeunea conchifolia occur predominately on the bark of hardwood trees.
Several northern bryophytes, such as the moss Dichodontium pellucidum and two species of the liverwort Marsupella, reach the southern limit of their distribution in the sandstone ravines of the Cumberland Plateau. Presumably, the cool microclimate in these sandstone ravines has provided conditions favorable to the survival of northern species that were pushed south during the last ice age. Coincidentally, these same sandstone ravines serve as the northernmost limit of some tropical bryophytes, including the ruggedleaf schlotheimia moss (Schlotheimia rugifolia) and the liverwort Cololejeunea cardiocarpa.
Forested ravines in south Alabama are also rich in bryophytes, including many that are most common to tropical regions, such as the moss Pyrrhobryum spiniforme and the liverwort Mastigolejeunea auriculata. There is a site in Dale County on the Choctawhatchee River in which liverworts are so abundant that it has been given the name "liverwort gorge" in the botanical literature. Humid ravines such as this, as well as creek banks, and springs, are home to little known species such as the liverwort Lophocolea appalachicola, which is endemic to the southeastern U.S. Coastal Plain. Bryophytes are scarce in dry pine forests, however, and are virtually absent from coastal dunes, except for the moss, Tortella flavovirens, which is a salt-tolerant species found on the Alabama coast.
The sphagnum mosses, commonly known as peat moss in the horticulture trade, are perhaps the best known types of moss and are an important component of pitcher plant bogs in south Alabama. The tremendous water-holding capacity of the sphagnum mosses helps to sustain boggy terrain during times of drought, and thus these mosses are an important component to these unique ecosystems. Sphagnum is found throughout the state in flatwoods, on stream banks, and hanging from sandstone cliffs. Sphagnum is reported to have been used during the Civil War as a dressing for wounds and is an important component in potting soil and other horticultural uses.
The ecological importance of bryophytes in Alabama has not been clearly established. To some extent bryophytes serve as a seed bed for vascular plants and help prevent soil erosion. Some bird species, such as eastern phoebe and the eastern robin, use mosses as a nest-building material. Their most important ecological role, however, is as a habitat for countless invertebrates and other microscopic life. Tiny terrestrial arthropods, including mites, pseudoscorpions, and springtails, are common moss inhabitants. One of the most interesting habitats can be found among some of the terrestrial mosses, especially moss on tree trunks. After a rain, aquatic invertebrates such as rotifers, nematodes, and water bears swim and crawl within tiny films of water held within the moss mat. Almost all mosses found on trees throughout Alabama contain these aquatic animals, which are uniquely adapted to short periods of water availability. As the moss dries, the animals also dry out and become dormant.
The earliest scientific efforts to collect and study Alabama's bryophytes were made in 1843 in Mobile by William Starling Sullivant of Ohio, the father of American bryology. Charles T. Mohr, a scientist and naturalist in Mobile, produced the first and only comprehensive report of Alabama's bryophytes, which was published posthumously in 1901 in Plant Life of Alabama. Mohr reported 153 species of mosses, 44 species of liverworts, and four species of hornworts at the turn of the nineteenth century. Today, the number of species reported in Alabama has increased to roughly 300 mosses and 100 liverworts, but the number of hornwort species has remained the same. Additional species are still being discovered in the state and are recorded in various scientific publications and added to the collections of herbaria.
Although no bryophytes are unique to Alabama, several species are considered rare and of conservation concern within the state borders. For example, the mosses Pleurozium schreberi and Fissidens hyalinus and the liverwort Blasia pusilla are common in other parts of the United States but very rare in Alabama. Others, such as the moss Homaliadelphus sharpii and the liverwort Cheilolejeunea evansii, are globally rare. In Alabama, threats to the survival of bryophytes generally result from loss of habitat owing to human activity.
Paul G. Davison
University of North Alabama
Published August 29, 2007
Last updated April 25, 2012