Mosses: Characteristics, Reproduction and Economic Importance


Mosses: Characteristics, Reproduction and Economic Importance

Mosses belong to the division Bryophyta and the class, musci. Mosses are land plants which grow on moist ground under the shade of big trees as epiphytes; on packed wet blocks, and or old block walls and rocks.

Funaria (a common moss species) grows in turfs to form a green carpet. Sometimes, relatively extensive areas may be completely covered by it, particularly the sites of old bonfires in woodlands. 

The moss is often able to colonise such burnt patches remarkably quickly. This is an indication of its measure of success as a land plant.

Mosses lack true roots, stems and leaves; they are parenchymatous (i.e. they have parenchyma tissues), they lack vascular tissue. The gametophyte (the haploid, gamete producing phase of the plant) is dominant and nutritionally independent, whereas the sporophyte (the diploid, sporeproducing phase of the plant) is permanently attached to the gametophyte.

The mature gametophyte is usually erect and radially arranged. The spores are released from the sporophyte by a tranverse splitting of the sporangium or capsule. Mosses play an important role in nature.


Characteristics of Mosses

Do you remember that living organisms have some characteristics or features that are peculiar to them? Mosses as living organism have their peculiar characteristics.

The following characteristic features of mosses below:

1. The plant is small and erect.

2. Persisting vegetative body is attached to subsratum.

3. Body consists of attaching and absorbing rhizoids and, aerial part for photosynthesis.

4. Dichotomous branching. Growth is from a single cell or row of cells.

5. Low degree of tissue differentiation.

6. Well defined sexual reproduction.

7. Sex organs are the antheridia and archegonia.

8. Fertilization is with biflagellate male gametes.

7. Plant body is one haploid gametophyte.

8. Diploid sporophyte (sporogonium) is partially or wholly dependent upon the gametophyte.

9. Spores are of one type (homosporous) Spores usually germinate into an intermediate structure (protonema). Mainly terrestrial but in wet environment.

10. Commonly found on old damp walls, tree trunks and wet ground. They are gregarous, forming green carpet.

11. Small in size measuring a little more than one centimeter in height.

12. Axis is short with spiral, minute green leaves. True roots are absent but rhizoids are present for absorption and anchorage.

13. Rhizoids are made of cells not differentiated into tissues and organs. The stem (no conducting tissues) is short, slender and often with a branching stem, covered by remains of archegonia rosette of leaves neck at tip of male shoot cluster of leaves at tip of female shoot; surround archegonia (female sex organ) 'leaf' - well developed with conspicuous midrib; leaves spirally arranged 'stem capsule - photosynthetic; green when immature, orange-brown when ripe annulus - cells here force off operculum when capsule is ripe operculum - lid of capsule sporophyte semi-dependent on gametophyte  Access Biology simple leaves spirally arranged along the stem and its branch.

The two branches of stem are differentiated into male and female branches. 

The sporogonium consists of a long seta (stalk) and a pear-shaped capsule. 

The rhizoid, stem and leaves all together form the gametophyte. 

The gametophyte alternates with the sporophyte during the life cycle. This is called alternation of generations.


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Reproduction in Moss

You will find reproduction in moss very interesting. Would you like to know how reproduction occurs in moss plant? The moss plant (e.g. Funaria) bears separate male and female parts at maturity, biciliate spermatozoa (antherozoids) and large ovoid eggs are formed at the top of the plants.

Reproduction takes place in the rainy season as male gametes swim in water into the archegonium (multicellular structure in which an egg is produced, a female gametangium).

Male gametes (antherozoids) are released by the male plants after rainfall when water covers the top of the plants growing in turfts.

Male gametes (antherozoids) swim in water into the archegonium on the female plant within the tufts. One antherozoid fuses with one egg in the archegonium of the top of a female plant. A zygote is formed on the top of the female plant.

The, zygote develops into a sporogonium which constitutes the sporophytic generation. This is the spore-producing structure which is partly dependent on the gamete producing structure for its nourishment.

The bryophytes (moss and liverworts) have two phases in their life history

1. The gametophyte phase which reproduces sexually by means of gametes

2. The sporophyte phase which reproduces asexually by means of spores

This phenomenon is known as the Alternation of Generations. It is very necessary for you to know more about the Antheridium, Archegonium, gametophyte, sporophyte and Alternation of generations and the roles they play in the development of a new moss plant.

The Antheridium

It is club-shaped. Inside are antherozoid mother cells (or androcytes) a mass of small cells surrounded by a simple layer of cells that form the wall or jacket. Each develops into a single antherizoid. Antheridium lid opens to liberate antherizoids. Antherizoids are minute, spirally coiled and bicilliate. They swim in films of water to the archegonium.

The Archegonium

It is flask-shaped. Consists of swollen portion (venter) and upper tube-like neck. Neck canal secretes mucilage and malic acid to attract antherizoids Fertilisation occurs in the venter to form zygote Zygote secretes thick walls to become oospore. Oospore germinates through the apex to form the sporogonium (sporophyte).

The Gametophyte

Bears reproductive organs. Male organs: the antheridium produces antherizoids. The female organ, the archegonium, borne on separate shoots/branches produces egg cell or ova. Both are protected by hair-like structures called paraphyses.


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Sporophyte - Inside the capsule

• The sporophyte produces spores.

• Consists of foot, seta and capsule.

• Capsule dehisces, spores are liberated and dispersed.

• Spores germinate.

• Under favourable conditions, spores germinate into short tube which forms a green muchbranched filament called protonema.

• Develop slender-brown rhizoids and small lateral buds.

• Buds develop into new moss plants.


Alternation of Generations

• Funaria shows two stages in its life cycle.

• The growing plant is the gametophyte.

• Sporogonium is the sporophyte.

• Fertilization leads to formation of sporophyte.

• By asexual production of spores, gametophyte germinates.

• Chromosomes are reduced to haploid number during spore formation.

• There is thus an alternation between the gametophyte and sporophyte phases.


Economic Importance of Mosses

Let us now consider the economic importance of mosses

1. Mosses grow and reproduce rapidly on a favourable substrate and under favourable environmental conditions. As they die and decompose, they form suitable humus on which other higher plants can grow. They, therefore, form a necessary step in the natural process of ecological succession that may lead to climax vegetation.

2. The bog or peat moss (sphagnum) actually consists of a mixture of plants of which the sphagnum forms the dominant vegetation. This plant colonises an acid environment. The plant, itself, has antiseptic properties for which reason it does not decay fast.

Thus, the plant debris accumulates as "peat" Peat is often dried and used as fuel. It is also useful in agriculture because of its water-holding capacity for which it is frequently mixed with sandy or humus-poor soils. There are reports that sphagnum has been sterilised and used for wound- dressing because of its waterholding characteristics.

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