Plant Kingdom - Notes | Class 11

Plant Kingdom Notes - Bryophytes

Bryophytes

Called amphibians of the plant kingdom because they live in soil but need water for sexual reproduction.
Occur in damp, humid, and shaded localities.
Body more differentiated than algae, thallus-like, prostrate or erect, attached to the substratum by unicellular or multicellular rhizoids.
Lack true roots, stem, or leaves but may have root-like, leaf-like, or stem-like structures.
Main plant body is haploid, produces gametes, called a gametophyte.
Sex organs are multicellular.
Male sex organ (antheridium) produces biflagellate antherozoids. Female sex organ (archegonium) is flask-shaped, produces a single egg.
Antherozoids are released to water, meet archegonium, and fuse with the egg to form a zygote.
Zygotes do not undergo meiosis immediately, produce a multicellular sporophyte.
Sporophyte is not free-living, attached to the photosynthetic gametophyte, derives nourishment from it. Some sporophyte cells undergo meiosis to form haploid spores, which germinate to form gametophyte.

Some mosses provide food for herbaceous mammals, birds, and other animals.
Species of Sphagnum (a moss) provide peat, used as fuel and as packing material for trans-shipment of living material due to its water-holding capacity.
Ecologically important in plant succession on bare rocks/soil. Mosses and lichens decompose rocks, making the substrate suitable for higher plants.
Form dense mats on soil, preventing soil erosion.

Bryophytes are divided into liverworts and mosses.

Grow in moist, shady habitats like banks of streams, marshy ground, damp soil, bark of trees, and deep woods.
Plant body is thalloid, e.g., Marchantia. Thallus is dorsi-ventral, closely appressed to the substrate. Leafy members have tiny leaf-like appendages in two rows on stem-like structures.
Asexual Reproduction:
- By fragmentation of thalli or formation of gemmae (sing. gemma).
- Gemmae are green, multicellular, asexual buds in gemma cups on thalli. They detach and germinate to form new individuals.
Sexual Reproduction:
- Male and female sex organs on same or different thalli.
- Sporophyte is differentiated into foot, seta, and capsule.
- After meiosis, spores are produced in the capsule, germinate to form free-living gametophytes.

Predominant stage is the gametophyte, with two stages:
- Protonema stage: Develops from a spore, creeping, green, branched, often filamentous.
- Leafy stage: Develops from secondary protonema as a lateral bud, with upright, slender axes, spirally arranged leaves, attached to soil by multicellular, branched rhizoids. Bears sex organs.
Vegetative Reproduction:
- By fragmentation and budding in the secondary protonema.
Sexual Reproduction:
- Antheridia and archegonia produced at the apex of leafy shoots.
- After fertilisation, the zygote develops into a sporophyte with foot, seta, and capsule.
- Sporophyte in mosses is more elaborate than in liverworts. Capsule contains spores formed after meiosis.
- Mosses have an elaborate spore dispersal mechanism.
E.g., Funaria, Polytrichum, Sphagnum.