Bryophytes are also called Amphibians of the plant kingdom. They include mosses and liverworts which grow commonly in the moist shaded area in the hills. They show haplo-diplontic life cycle.
- These are called Amphibians of the plant kingdom because they can live on soil but for sexual reproduction, they depend on water.
- The embryophytes without vascular tissues.
- Mostly occur in damp, humid, and shaded areas.
Body Organization in Bryophytes:
- Thallus-like, prostrate or erect, found attached to the substratum by unicellular or multicellular rhizoids.
- Lack of true roots stems, or leaves.
- The main plant body is a free-living gametophyte (dominant phase), Bryophytes plant body is haploid.
Reproduction in bryophytes:
Gamet production takes place, so it is called gametophyte. sex organs are multicellular.
- Vegetative Reproduction: Very common and occurs through fragmentation, tubers, gammae, buds, and adventitious branches.
- Sexual Reproduction:
- Antheridium– Male sex organ- single, coiled, biflagellate antherozoids or spermatozoids produced by them.
- Archegonium– A female sex organ- is a flask-shaped and swollen base called a venter and upper elongated neck, producing a single egg.
- Antherozoid is released into the water and there it comes in contact with archegonium.
- An antherozoid fuses with eggs to produce a zygote and a multicellular body is produced by them which is called the sporophyte. Sporophytes get attached to the photosynthetic gametophyte and get nourishment from it.
- Some cell of the sporophyte follow reduction division i.e. meiosis and produces haploid spores. By the germination of these spores, the gametophyte is produced.
Alternation of Generation in bryophytes:
The bryophytes show heteromorphic or heterologous alternation of generation in their life cycle, i.e. haplo-diplontic life cycle. They also exhibit the phenomenon of apospory and apogamy.
- Apospory: The process by which gametophyte develops from the vegetative cells of the sporophyte.
- Apogamy: Sporophyte develops from gametophyte without gamete union.
Economic Importance of Bryophytes
- In general, Bryophytes are of little economic importance. Some mosses provide food for herbaceous mammals, birds, and other animals.
- Sphagnum species of moss, provide peat which is used as fuel and packing material for transshipment of living materials because they have the capacity to hold water.
- Mosses along with lichens are the first organisms to colonize rocks and for this are of great ecological importance.
- they decompose rocks and make substrate suitable for higher plant growth.
- Mosses also prevent soil erosion by forming dense mats on the soil which reduces the impact of rainfall on the soil.
Classification of Bryophytes
The bryophytes are divided as
- Hepaticopsida- Liverworts
- Anthocerotopsida- Hornworts
- Bryopsida- Mosses.
Habitat: The liverworts grow in moist, shady habitats like banks of streams, marshy areas, damp soil, the bark of trees, and also in deep woods.
Plant body: The body of a bryophyte plant is thalloid. The thallus is dorsiventral and closely appressed to the substrate. Example- Marchantia.
- Asexual reproduction by fragmentation of thalli, or bay the formation of a specialized structure called gemmae.
- these are green in colour, multicellular, asexual buds that develop in small receptacles called gemma cups and are located on thalli.
- The gemmae get detached from the parent body and germinate into new individuals.
- Sexual reproduction– during sexual reproduction both male and female sex organs are produced either on the same or different thalli.
- Sporophyte gets differentiated into a foot, seta, and capsule- e.g. Marchantia. (only capsule- Riccia)
- Spores are produced within the capsule after meiosis and germinate forming free-living gametophytes.
- Examples: Riccia, Marchantia, Porella, Pellia, Sphaerocarpus, etc.
The Hornworts are bryophytes consisting of a hornlike elongated structure, ie. sporophyte. The plant body of hornwort is a haploid gametophyte stage. Mostly they are found in damp or humid places.
Some important characters of Hornworts:
- Thalloid, aseptate Zhizoids gametophyte is found.
- Sex organs are present on the dorsal surface of the thallus.
- Sporophytes differentiated into foot, short-meristem attic region, and capsule.
- Examples of hornworts: are Anthoceros, Notothylus, Megaceros, etc.
Characteristic features of mosses:
The mosses typically form dense green clumps or mats, mostly in damp or shady locations. They are small (a few centimeters tall) herbaceous (non-woody) plants that absorb water and nutrients mainly through their leaves and harvest CO2 and sunlight to create food by Photosynthesis.
Moss gametophytes consist of stems that may be simple or branched, and upright or prostrate. The leaves of mosses are simple, usually a single layer of cells without internal air spaces, often with thicker midribs.
The prime stage of a moss’s life cycle is gametophytic which contains two stages:
- Protonema stage: developed by a spore directly. It is green, creeping, branches, and filamentous stage.
- leafy stage: Developed by secondary protonema as a lateral bus and consisting of upright, slender axes bearing arranged leaves, attached to the soil through multicellular and branched rhizoids. Sex organs are born by this stage.
Reproduction in mosses
- Vegetative reproduction by fragmentation and budding during secondary protonema.
- Sexual reproduction as the sex organs antheridia and archegonia are produced at leafy shoots.
- The zygote develops into a sporophyte after fertilization.
- Sporophytes consist of a foot, seta, and capsule, which contains spores.
- spores are formed after meiosis.
Some common examples of mosses: are Funaria, Polytrichum, and Sphagnum.
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