Mosses

Mosses are small, soft, flowerless Plants. Mosses are unique Bryophytes in the sense that they have Stomata, cells specialized for photosynthetic gas exchange, on their Sporophytes. There are approximately 12,000 Species of Moss classified in the Bryophyta. Mosses existed as early as the Permian Period  (299 to 251 million years ago), and more than 100 Species have been identified from fossils of the Paleogene and Neogene periods (65.5 to 2.6 million years ago). Mosses are found chiefly in areas of dampness and low light. Mosses are common in wooded areas and at the edges of streams. Mosses are also found in cracks between paving stones in damp city streets, walls, rocks and logs forming cushions just a few millimetres thick. Some Species have even adapted to urban conditions and are found only in cities. A few Species are wholly aquatic, such as Fontinalis antipyretica, and others such as Sphagnum inhabit bogs, marshes and very slow-moving waterways. A collection of Mosses is known as Mossery. Decaying Moss in the genus Sphagnum is a major component of peat, which is 'Mined' for use as a fuel, as a horticultural soil additive, and in smoking malt in the production of Scotch whisky. Cristatum and Subnitens are the Species which are harvested while still growing and is dried out to be used in nurseries and horticulture as a Plant growing medium. Moss is used as a Christmas decoration in Mexico. Physcomitrella patens, a Moss is increasingly used in biotechnology with uasgae in crop improvement, human health and safe production of complex bio-pharmaceuticals. Moss is eaten by Reindeer's because it contains a chemical that keeps their blood warm.

Scientific Classification

Kingdom - Plantae.
Division - Bryophyta.

Classification and Types of Mosses

The Mosses are grouped as a single Division, now named Bryophyta, and divided into 8 Classes:

1.  Takakiopsida - There are only 2 Species of this Class. T. ceratophylla and T. lepidozioides.

2.  Sphagnopsida - It includes a single subclass Sphagnidae, with 3 Orders.

Orders

• Sphagnales - It contains only the Genus Sphagnum, with all but 2 of the Species.

• Ambuchananiales - It contains a single living Species.

• Protosphagnales - It contains a single fossil Species.

3.  Andreaeopsida - It includes two Genera:

Genera

• Andreaea - It contains about 100 Species.

• Acroschisma.

4.  Andreaeobryopsida - It includes a single Species - Andreaeobryum macrosporum.

5.  Oedipodiopsida - Oedipodium is the only genus of Moss in the family Oedipodiaceae. It contains a single Species - Oedipodium griffithianum. This Species is distributed in cooler climates of Eurasia, North and South America, and islands in the northern Atlantic.

6.  Polytrichopsida - It includes 2 Orders.

Orders

• Polytrichales.

• Tetraphidales.

7.  Tetraphidopsida - It includes only the 2 Genera:

Genera

• Tetraphis - Tetraphis geniculata, Tetraphis pellucida are the 2 Species.

• Tetrodontium - Tetrodontium brownianum, Tetrodontium repandum are the 2 Species.

8.  Bryopsida - It is the largest Class of Mosses, containing 95% of all Moss Species. It consists of approximately 11,500 Species, common throughout the whole World.

Characteristics and Physical features of Mosses

• Non-Vascular Plants - Mosses lack Vascular system i.e. they lack specialized Vascular Tissue (xylem and phloem) for internal water and food conduction and support. They are also known as Bryophytes as they possess no true roots, stems, or leaves. Their leaf-like structures are called Phyllids. They are typically only one cell thick, although Phyllids in some Species are several cells thick.

• Absence of Flowers and Seeds - They do not have flowers or seeds.

• Presence of Multicellular Rhizoid - Mosses are the only Plants that have a Multicellular Rhizoid which is a root-like subterranean tissue that absorb water and nutrients from the soil.

• Radial Symmetry - Mosses have Radial Symmetry i.e. if they are cut down, the long axis of an individual gives two similar halves.

• Tendency to grow in Clusters - They commonly grow close together in clumps or mats. Moss patches can make its own soil from particles in the environment.

• Small Stature - They are small land Plants that do not grow to large sizes.

• Ability to revive with very Less Water - Mosses are amazingly resilient and versatile group of Plants. During summer, Moss can reduce its metabolism to almost zero in order to survive.  They can survive periodic dry spells, reviving when Water becomes available. If we dry them out completely, subject them to heats of 70 C and the apply water, they will spring back into vibrant life again. There have been instances where dried museum specimens revived after many years storage, just by the simple application of a few drops of water.

• Preference for Moist Environment - All Mosses need water to complete their life cycle. In wet conditions, the Moss acts like a sponge, providing semi-aquatic conditions for a whole variety of other minute creatures, as well as a wonderfully damp nursery for germinating tree seedlings and other flowering Plants. The Sphagnum or Peat Moss can soak up 25 times its own weight of water.

• Habitat Indicators - Mosses can also be extremely useful as Habitat Indicators.  Many Mosses have very distinct preferences for either Acid or Alkaline Soils. For example, Mosses such as Tortella Tortuosa and Neckera crispa prefer soils with a high lime content and pH. Others such as Campylopus paradoxus favour acidic soils, while Sphagnum moss can thrive in bogs with a soil pH as low as. This information is useful to know a soil type and it's improvement.

• Size - Mosses may range in size from microscopic forms to Plants more than 1 m (40 inches) long.

Geographical Range and Habitat

They are world-wide in distribution and can be found at sea level as well as the highest altitudes occupied by Plants. Although they can occur in deserts or be submerged in water, most Mosses occupy moist, shaded habitats.

History and Evolution of Mosses

The earliest known Moss fossil dates back to early Carboniferous Period (about 320 million years ago). Confirmed Moss fossils have been recovered from as early as the Permian of Antarctica and Russia, and thereby dating them back to Carboniferous Mosses. The fossil record of Moss is sparse, due to their soft-walled and fragile nature. An examination of extant Species indicates that Bryophytes are a Polyphyletic group i.e. it consists of organisms but not their common ancestors. They appear to have evolved from more than one ancestral line. Most botanists believe that Mosses evolved from aquatic ancestors but there is no uniformity of theories regarding their evolutionary ancestry. It is generally believed that Mosses evolved from a simpler filamentous Green Alga. Although Bryophytes appear intermediate in complexity between Algae and Vascular Plants, they are unlikely to be an evolutionary missing link between these two groups.

Life Cycle of Mosses

A typical Moss alternates between a Haploid Gametophyte and Diploid Sporophyte Phases. Haploid and Diploid refer to the number of Chromosomes in the Cells of an organism.  A Gametophyte is the Haploid (N) generation that produces Gametes. The Sporophyte is the Diploid (2N) that produces Spores by Meiosis. The Gametophyte of a Moss is usually the largest and longest-lived generation of the Moss life cycle. Gametophytes of Mosses have Rhizoids, slender, root like structures that anchors the Moss in place. The Gametophytes are the photosynthetic part of a Moss. The Sporophyte of a Moss is usually smaller than the Gametophyte and is attached to the Gametophyte. Sporophytes lack Chlorophyll, they depend on the photosynthetic Gametophyte for food. The Sporophyte consists of a foot that anchors it to the Gametophyte and a Stalk. The Stalk grows up from the foot and resembles a Street Lamp. Atop the long, slender Stalk is a Capsule. A Capsule is the structure of a Moss that forms Haploid Spores.

Reproduction

The egg and sperm of Mosses form in different reproductive structures. The sperm-producing organ of a Moss is called Antheridium. Each Antheridium produces many sperm which are tadpole-like sex cells. The Egg-Producing Organ of a Moss is called Archegonium. Each flask-shaped Archegonium forms one egg. The Archegonia form on branches of the Gametophyte. Gametophyte is a phase of Plant life cycles in which the Gametes, i.e., egg and sperm, are produced. Both the Archegonia and Antheridia are part of the Gametophyte. Like all Bryophytes, Moss Gametes are surrounded by a jacket of sterile cells. The Sterile Cells are an important adaptation that protects the Gametes from drying out and dying. Eggs of Mosses are large but cannot move. But sperms are smaller and have Flagella which enable them to reach the eggs by swimming through water. For most Mosses, Fertilization can occur only during or soon after rain or after flooding, when the Gametophyte is covered with water. The sperms swim to the egg by following a trail of chemicals released by the egg in the water. Fertilization produces a Zygote that undergoes Mitosis and becomes a Sporophyte. Sporophyte is a Stalk that grows from the ova. On top is a Capsule holding thousands of spores. When the Sporophyte matures, cells inside the Capsule undergoes Meiosis and forms Haploid Spores (having 2 sets of chromosomes). These spores begin the Gametophyte Generation. When spores are mature, the Capsule opens and spores are carried off by wind. If a spore lands in a moist place, it sprouts and forms a new Gametophyte.