Table of Contents
What are Bryophytes?
Bryophytes are the non-vascular plants, which do not contain true leaf and thus, does not possess phloem and xylem. They are found usually on the rocks and can thrive in hot as well as snowy conditions and few of them might live in places which are dark and contain moisture.
Examples are hornworts, mosses and liverworts. As they require water from the environment, they get it from rain. For bryophytes water is very important as it helps in reproductive process.
For example, mosses have hydroids in the center, which are water conducting cells and while others have leptoids, which are food conducting cells. As they do not possess the vascular tissues, they are not quite in length and are very mushy in structure and thus are flexible.
The gametophyte in non-vascular plants, consists of leaf’s and can be seen, whereas the sporophytes will result in generation of spores which are seen at the leaf’s tip of the gametophyte.
All the bryophytes have same life cycle and number of chromosomes and can be divided into three groups on the basis of mode of reproduction and their appearance.
Bryophytes Groups
i. Liverworts
They belong to the division Hepaticophyta, where wort stands for herbs during the ancient times and these were used in treating diseases of liver. In structure, they are flat and have a body like the leaf which is the thallus. They do not contain stomata, which is seen in mosses and hornworts.
However, majority of the liverworts look like mosses, and are more complexed. Beneath is the rhizoid present, which is made from single cell and appears like roots which connects the plants to the roots and the base. The gametophyte generation is the thallus which will produce spores. The cell walls are thick and the outer surface is mushy.
a) Thalloid Liverworts
An example of liverwort is Marchantia, which is seen after fire on slightly wet mud. They can reproduce through both the modes. In asexual mode of reproduction, tiny tissue pieces called gemmae, which are formed from gametophytes upper surface, are separated from thallus.
As water drops on these gemmae cups, they separate at a distance of 3 feet far from parent. The further growth of gemmae when it comes out of the cup is stopped by lunularic acid, and will further form into thallus.
In sexual reproduction, male and female gametophytes come in contact with the spores, resulting in the formation of umbrella like structure on stalks, gametongia on the gametophores. The shape of a male gametophore is like disc, whereas the female looks like the spikes on the wheel.
The gametangia of males are called the antheridia, which comprises of sperms and are formed from the upper surface of antheridiophore. The gametangia of females consist of single egg and in appearance looks like flask.
These are produced in lines and there are upside down through the archegoniophore and as the drops of rain fall on its sperms would be liberated. The archegoniophore is linked to the multicellular embryo. The knob-like foot of the archeniophore is attached to sporophyte through the seta, which is a thick stalk.
Spore cells within the capsule perform meiosis and produce haploid spores, in few cases they do not undergo this process and remain diploid and form elaters, which react when changes regarding humidity are seen.
To spread the spores, the elaters will twist and the juvenile sporophytes posses a cap which is formed from tissues and is known as calyptra. However, in some cases when the thallus decomposes, then only spores will be liberated of liverworts.
b) Leafy Liverworts
These types of liverworts exist in forest and have two layers, where leaves overlaps and in the body they contain oil. As they don’t possess any folding which will hold the water and thus, tiny animals reside. Antheridia and archegonia are produced by the male and female gametangia and further maturation of spores result in production of protonema, which forms a plant and is photosynthetic.
ii. Hornworts
The spores of hornwort in appearance are like the horns of cattle which are green in color, on the maturation of spores. They are present in areas which have moisture and are dark, few of them survive in cold conditions and are also seen on trees. In between 1-8, is the number of chloroplast present and is usually one and resemble the green algae.
a) Sexual Reproduction
Through sexual reproduction as well, hornworts can produce where plants can be bisexual, where the antheridia and archegonia reside on same plant and in unisexual, mosses and liverworts. Sporophytes contain stomata but not seta and stalks. When they come out of the gametophyte generation, they are very small and look like the handle of the broom.
Sporophyte grows in size until appropriate conditions are achieved to obtain spores. As the tip separates, spores will fall off here and there, where the horn will fall off into ribbon segments.
a) Asexual Reproduction
The asexual reproduction occurs through fragmentation or by formation of lobes, which will detach from thallus.
iii. Mosses
Moss further has three sub-classes, which are rock mosses, true mosses and peat mosses. All of these three classes have same life cycle. Moss leaves are haploid and don’t contain veins and mesophyll, but does contain chloroplast in the shape of lens. Chloroplast is absent in the midrib area.
The water storage in the cells is transparent, which soaks water and gives the moisture to the required plant. Mosses have roots which are called the rhizoids, which aids in water absorption, although majority of the water reaches through the capillary action.
a) Sexual Reproduction
The gametangia in mosses are usually on the same plant, whereas the archegonia and antheridia are formed on the tips of the leaves. Within the antheridia, sperms are formed and zygote results in an embryo, upon fertilization, which is also linked to the foot.
From the embryo, sporophyte is formed, along with the seta, capsule and stalk, where the capsule is coated with the calyptra, and within the capsule meiosis is taking place to produce spores, which are liberated at the capsule tip. Once the spores matures, peristome which is protected by operculum, falls off and after germination, budding it will form into a moss.
b) Asexual Reproduction
Moss also undergoes fragmentation, which forms protonema, which matures and will form a moss.
Bryophytes Citations
- Valuable Fatty Acids in Bryophytes-Production, Biosynthesis, Analysis and Applications. Plants (Basel) . 2019 Nov 19;8(11):524.
- Bryophytes: Hoard of remedies, an ethno-medicinal review. J Tradit Complement Med . 2016 Apr 4;7(1):94-98.
- Bryophytes as a source of bioactive volatile terpenoids – A review. Food Chem Toxicol . 2019 Oct;132:110649.
- Figures are created with BioRender.com
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