Plant Kingdom

BRYOPHYTES

Habits & Habitats: Bryophytes include the various mosses and liverworts which are usually found in moist shaded areas in the hills. Bryophytes are also called amphibians of the plant kingdom because they can live on soil but need water for sexual reproduction. They are usually found in damp, humid and shaded localities.

Characteristics: The plant body is thallus-like and can be prostrate or erect. The plant body is attached to the substratum by unicellular or multicellular rhizoids. True roots, stem or leaves are absent. However, root-like, leaf-like or stem-like structures may be present.


Reproduction: The main plant body is haploid in bryophytes. The main plant body is called gametophyte because it produces gametes. Sex organs are multicellular. Male sex organ is called antheridium and produces biflagellate antherozoids. The female sex organ is called archegonium and produces a single egg. Antherozoids are released into water for fertilization. After fertilization, zygote does not immediately divide meiotically. Zygote produces a multicellular body called sporophyte. Sporophyte is attached to the photosynthetic gametophyte so that it can get nourishment from the gametophyte. Some cells of the sporophyte undergo meiosis to produce haploid spores. The spores germinate to produce gametophyte.

Economic Importance of Bryophytes:


LIVERWORTS

Characteristics: They usually grow in moist and shady habitats. The plant body is thalloid. Thallus is dorsiventral and closely appressed to the substrate. Some members have tiny leaf-like appandages in two rows on the stem-like structures.

female thallus of marchantia

Reproduction: Asexual reproduction takes place by fragmentation, or by formation of specialized structures called gemmae. A gemma is a green, multicellular, asexual bud. A gemma develops in small receptacles called gemma cup. The gemma gets detached from the parent body and germinates to form a new individual.

male thallus of marchantia

In case of sexual reproduction; male and female sex organs are produced either on the same or on different thalli. The sporophyte is differentiated into a foot, seta and capsule. Spores are produced after meiosis. These spores germinate to produce free-living gametophytes.


MOSSES

Characteristics: Gametophyte is the predominant stage of the life cycle of moss. The gametophyte consists of two stages, viz. protonema stage and leafy stage.

Protonema develops from the spore. It is creeping, branched and usually filamentous.

The leafy stage develops from the protonema as a lateral bud. The leafy stage consists of upright, slender axes bearing spirally arranged leaves. It is attached to the soil through multicellular and branched rhizoids. The leafy stage bears the sex organs. Reproduction: Vegetative reproduction takes place by fragmentation and budding in the secondary protonema.

In case of sexual reproduction, antheridia and archegonia are produced at the apex of the leafy shoots. After fertilization, the zygote develops into a sporophyte. The sporophyte consists of a foot, seta and capsule. The capsule contains spores. Spores are formed after meiosis. There is an elaborate mechanism of spore dispersal in mosses.

Common Examples: Funaria, Polytrichum and Sphagnum



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