Moss
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The various mosses need moisture and function less well in sun, they can, some of the time be found on the north sides of trees. Most mosses need damp and shade to develop, and so are sometimes thought to be halfway between aquatic plants and terrestrial ones. Mosses, along with liverwort and hornwort, are part of the phylum Bryophyta (which means "moss plant" in Greek). These are known for lacking a vascular system and for having an alternate generation reproductive system that uses spores. There are at least 16,000 recognized moss species in the world divided into the true mosses and sphagnum moss (which is often called peat moss).
Anatomy
The tiny, green moss plant is nearly always seen in large, dense groups. The leaves are usually one cell thick and the plants have tiny rootlets which are connected to each other because many plants grow from a long horizontal pipe like structure called the protonema. The gametophytes grow vertically and provide the cushioned stems that we associate with moss.
Moss plants do not have tubes (or what is called vascular systems) to carry sap or liquids and so use a sponge-like system that lets water diffuse to the tissues. Mosses cannot grow very tall because of this. The sponge effect makes sphagnum moss very useful to hold water to keep plants moist during shipping, or to absorb liquid in surgical dressings.
Mosses are similar to liverworts who have thicker leaves that generally lie flat on the ground. Irish moss is really a kind of seaweed, and club mosses are related to ferns and are not really mosses. Reindeer moss is really a kind of lichen.
Reproduction
Mosses do not reproduce by flowers or seeds but by producing spores. One generation of the moss plant is called the gametophyte plant and is either male or female. A fertilized egg cell develops into the second generation called the sporophyte which grows out of the top of the female gametophyte and develops the spore capsule. When the spore capsule breaks and scatters the tiny, dust-like spores, some spores land in a good damp spot, and grow into a tube-like protonema which grow new gametophytes. In one bunch of moss, both generations will be present at any one moment.
There are two gametophytes, male and female. The female plants provide an egg cell at the top (in the archegonia), and the male plants develop sperm cells with cilia (in the antheridia) which swim through the film of water on the moss to fertilize the egg cell. This is one reason the mosses need dampness to grow.
This alternation of generations seems complicated, but is a system used also by ferns and by liverworts.
Ecology
When mosses are dry they turn brown, but often come back to life as soon as they become wet again. Sphagnum moss can gradually fill up a whole lake with moss. When moss continually sinks to the bottom, it can create peat deposits like those found in England and Ireland. Bergman cites a reference which states that peat bogs in the northern countries cover an area half as large as the United States.
Moss is important in plant succession as plants recolonize volcanic rock or rocks stripped by floods or by fires. First come the lichens which break down rocks by acid, then comes mosses which grow in damp cracks in the rock that have thin layers of soil. Mosses build up the soil thickness until shrubs can take hold, but the shrubs shade out the mosses. Mosses are a necessary step in the development of soil.
Difficulties for Evolution
It is difficult for evolution to detail the mechanism by which water plants moved onto land. This development of land plants is already a difficult one for evolution. Moss would be a good intermediate step since it has no vascular system for carrying water to tissues. Mosses are found in fossils that are very early in the evolutionary time scale, and change is static up to the present. Thus mosses are either very successful, or an evolutionary dead end, or both. Evolutionists must postulate that somewhere small groups of mosses were somehow stressed to evolve into land plants, but have difficulty giving reasonable scenarios. Some have thought they developed from algae or ferns, while others think they have somehow been reduced from a vascular plant (like Rhyniophyta). The wide range of possibilities show difficulty for detailing plant evolution and that of the mosses.
Since mosses are so important in the succession of plants that develop soil from rock, they seem to fit into the web of life as a necessary component. The interdependency of plants and animals is perfectly reasonable for creation, but difficult to describe in terms of evolutionary development. Evolution must describe many successive systems that are all functionally interdependent and yet result in the complex web of life we see today.
References
- Moss Wikipedia
- Moss Information eSSORTMENT
- Bryophyte Natural Perspective
- Bryophyta Hort & Crop Science Home
- The Critically Important Plants Called Mosses by Jerry Bergman. CRSQ 35(1):27-30