Plants may be informally grouped into three categories based on structure and mode of reproduction: nonvascular spore plants which are simple in structure (no vascular system) and reproduce by spores, vascular spore plants which are advanced in structure (possess a vascular system) but reproduce by spores, and vascular seed plants which are advanced in structure and reproduce by seeds.
The nonvascular spore plants (known commonly and collectively as the bryophytes) encompass three divisions from the formal plant classification system: 6,000 species of liverworts, 100 species of hornworts, and 10,000 species of mosses.
Division Hepatophyta (Liverworts)
Liverworts are odd little plants that appear as small, flat green patches attached to the ground, although they may form large masses in favorable habitats such as moist, shaded rocks or soil, tree trunks or branches and a few even grow directly in water.
Liverworts were given their name in medieval times when the common belief in a “Doctrine of Signatures” held that a plant that resembled a certain part of the body was probably useful for treating ailments of that body part; some liverworts have an outline that resembles the liver, and thus they were thought useful in treating liver problems.
The Anglo-Saxon ending “-wort” means “herb”; it appears as a part of many plant names in the English language. There are two main groups of liverworts: the thallose liverworts, which are ribbon-like plants that grow flat against the ground and are lobed or rounded at one end where growth takes place and the leafy liverworts, which form simple leaf-like and stem-like structures similar to mosses.
When liverworts mature, they reproduce sexually and form spores or asexually by means of gemmae which contain clumps of cells that can grow into a new liverwort.
Division Anthocerophyta (Hornworts)
Mature hornworts resemble liverworts structurally. The sporophyte (spore-forming) phase of hornworts, however, differs greatly from the same phase in liverworts.
Division Bryophyta (Mosses)
The largest and most familiar group of bryophytes is the mosses. Mosses are a diverse group that is most abundant in moist shaded areas – swamps and bogs, near streams, and the floor of forests. These plants sometimes dominate the terrain to the exclusion of other types of plants over large areas of the far north and far south, as well as on rocky slopes above timberline in mountainous regions. A few species are even found on seaside wave-splashed rocks, although none is truly marine.
Many small tufted plants are mistakenly called “mosses” – “reindeer “mosses” are lichens, Spanish “moss” is actually a flowering plant related to the pineapple, and “seaweed” and Irish “moss” are algae.
There are three groups of mosses: the “true” mosses, which form dense mats that are said to be “cushiony” or “feathery” depending on their growth pattern and appearance; the peat mosses, whose gametophytes form large, bright green or occasionally reddish clumps in boggy ground, and the granite mosses, which are small blackish-green or dark reddish-brown tufted rock mosses that occur in mountainous or Arctic regions, often on granite rocks, which is the reason for their common name.
Mosses vary in appearance from miniature evergreen trees to small, filamentous plants that mass together to form the carpet of green we so often associate with the forest floor.
Sphagnum mosses are a group of peat mosses that thrive in the acidic water of bogs. Dried sphagnum moss absorbs many times its own weight in water and thus acts as a sort of natural sponge. Gardeners have found this particular property quite useful for maintaining adequate levels of moisture in the soil.
In certain environments the dead remains of sphagnum accumulate to form thick deposits of peat. Peat can be cut from the ground and then burned as fuel. In fact, peat has been used as a form of fuel in Ireland for many centuries. Peat moss is also useful in gardening. Gardeners add peat moss to the soil to improve the soil’s ability to retain water and to help loosen heavy clay soils.
The bryophytes are represented by three small groups of plants that are primitive both in structure and reproduction. Relegated to the shade and shadow of moist areas, liverworts, hornworts, and mosses are not well known and may not even be recognizable as true plants to most people.
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