Bryophytes

The common word for Bryophytes is Moss, which are the first land plants in context with evolution of plants. The branch of science that deals with Bryophytes is called Bryology. Please note that Mosses don’t have a vascular tissue such as Xylem and Phloem, which we find in plants of higher orders. Due to this, they are also known as Atracheates which means no trachea. In India, S R Kashyap did a commendable job in the studies of Bryphytes and that is why is called Father of Indian Bryology.

Amphibians of Plant Kingdom

Bryophytes are called the “amphibians” of the plant kingdom. They can live on land but for reproduction and fertilization, need water essentially.

The Bryophytes were the first plants in which alternation of generation was seen for the first time in the embryophytes as Gametophyte→Mitosis → gametes →Sporophyte → Spores → Meiosis →Gametophytes.

Bryophytes: Important Points

• One of the famous Bryophyte is Peat Moss. Its botanical name is Sphagnum. It grows in swamps and damp areas. This is one of the most economically important Bryophyte. In World War I, Peat moss was used as “dressing cotton’ for wounded soldiers. Peat is obtained from Sphagnum.
• Physcomitrella patens is increasingly used in biotechnology. Prominent examples are the identification of moss genes with implications for crop improvement or human health and the safe production of complex biopharmaceuticals in the moss bioreactor.
• Mosses play an important role in controlling soil erosion. They perform this function by providing ground cover and absorbing water.
• Mosses are also indicators of air pollution. Under conditions of poor air quality, few mosses will exist.
• Peat is used as fuel to heat homes and generate electricity. Bryophytes are among the first organisms to grow up in areas that have been destroyed by a fire or volcanic eruption.

Why Mosses are haploid in most of their lives?

Bryophytes commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems. Please note that in Bryophytes, the dominant phase of life is not the plant itself but one of its phases in reproduction called gametophytes. The only thing you need to remember is that gametophyte contains a single set of Chromosome and that is why the “Bryophytes are in Haploid state in most of their lives”.

At certain times, mosses produce spore capsules, which may appear as beak-like capsules borne aloft on thin stalks. These gametophyte produces male or female or both gametes ^{(term used for sperms or ovum lower plants)} by mitosis. When male and female gametes fuse, they make a diploid zygote, which develops by repeated mitotic cell divisions into a multicellular Sporophyte. This Sporophyte is diploid because it is a product of fusion of two haploid gametes. This Sporophyte is NOT independent in Bryophytes and needs to get nutritional support from the gametophyte.

Now, this diploid phase Sporophyte again produces sex cells via meiosis, which are called spores. During making of spores, the chromosome pairs are separated once again to form single sets. The spores are therefore once again haploid and develop into a haploid gametophyte. This is how the lifecycle of a Bryophyte goes on.