Bryophyte

Bryophyte are nonvascular, seedless plants that include mosses, liverworts, and hornworts. They are widely distributed and typically small compared to seed-bearing plants. They lack try roots, stems, and leaves, and instead possess specialized structures called rhizoids, which anchor them to various surfaces and aid in water and nutrient absorption through diffusion and osmosis. They play an important role in the environment by colonizing sterile soils, absorbing nutrients and water and release them slowly back into ecosystem, contributing to the new emergence of soil for plants to grow on.

Taxonomy

Bryophyte phylogeny is derived from fossil records and molecular sequencing or rRNA and morphology. There is still much unknown about the true phylogeny of this group, however it is hypothesized that they branched off of charophyte-coleochaete, which is the Groupon green algae that gave rise to vascular plant species [1].

Bryophytes belong to the division Bryophyta and are further divided into three main groups:

• Mosses (Phylum Bryophyta)

Mosses are green, clump forming plants. They are known to have leafs that are only one cell in width, attached to a stem which is responsible for water and nutrient uptake. Mosses absorb a lot of water and thrive in shaded environments, which is why they are often found in wet, forested environments as a result.

• Liverworts (Phylum Marchantiophyta)

Liverworts are very small plants with flattened stems, and undifferentiated leaves. They posses single-called rhizoids, which are responsible for attaching to surfaces, and nutrient/water uptake. They are different compared to the other two bryophytes due to there enclosed lipid membrane-bound bodies.

• Hornworts (Phylum Anthocerotophyta)

Hornworts are characterized by there long horn-like sporophyte that developed in its diploid stage. During the gamete stage, hornworts are flat, green plants. They are often found in damp environments.

However, after molecular evidence Bryophyta are no longer divided into three groups and only mosses represent the division of Bryophyta. Hornworts and liverworts are in their own divisions, Anthocerotophyta and Marchantiophyta respectively [1].

Characteristics

Bryophytes have many unique features, one of them being, they are small in size and can grow on many surfaces including the surface of rocks. They are primarily found in damp environments, but are also found in a variety of different climates and ecosystems. They can tolerate desiccation and quickly rehydrate when water becomes available. They often form into dense mats that create habitat and microclimates for many organisms.

Habitat

Bryophytes can be found in many habitats around the world, such as: wetlands, costal areas, forests, tundra, rocky outcrops. They thrive in damp and shady environments but can also be found in extreme environments such as deserts and the arctic.

Life Cycles

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Bryophytes have a life cycle which consists of alternating generations of haploid gametophyte and diploid sporophyte [2]:

1. The gametophyte generation produces gametes through mitosis. The haploid gametes are formed in specialized sex organs, the archegonia (female) and the antheridia (male)
2. The gametes are described as flagellated sperm, which have to transport through water diffusion, and then dispersed by insects.
3. Fertilization occurs when sperm from antheridia, fertilize eggs in archegonia.
4. The zygote develops into a diploid sporophyte, which remains attached to the gametophyte (fertilized egg).
5. The sporophyte produces spores through meiosis, inside the sporangium.
6. Spores are released, and under the right environmental conditions they will germinate into new gametophytes. This completes the life cycle.

Evolution

Bryophytes are suggested to be one of the earliest groups of land plants which evolved from aquatic adaptations to survive in terrestrial environments. This was estimated to have happened roughly 430 million years ago. Bryophytes played a crucial role in the colonization of land fro plants by providing habitats and facilitating soil formation through metabolic functions and nutrient cycling.

Uses

Bryophytes have various human uses and ecological significance. They help in soil formation and prevent erosion by stabilizing the soil and act as indicators of environmental health, as they are sensitive to changes in air and water quality. They are used as radioactive indicators. Bryophytes are used in horticulture for decorative purposes, such as in moss gardens or terrariums. They contribute to nutrient cycling in ecosystems by absorbing and retaining nutrients in their tissues. Some species of bryophytes have medicinal properties and have been used in traditional medicine, and pharmaceutical products.

References

[1] Bryophyte. 2023, March 31. . Encyclopædia Britannica, inc. https://www.britannica.com/plant/bryophyte.

[2] Editors, B. 2019, October 5. Bryophyte - definition, characteristics, life cycle and examples. https://biologydictionary.net/bryophyte/.

[3] (N.d.). . https://www.ias.ac.in/article/fulltext/reso/009/06/0056-0065.

[4] PerezJI. “Bryophytes.” Smithsonian Tropical Research Institute, Smithsonian Tropical Research Institute, 28 Aug. 2024, https://stri.si.edu/story/bryophytes#:~:text=Bryophytes%20thrive%20in%20damp%2C%20shady,by%20spores%20instead%20of%20seeds.