What are Bryophytes?

A group of plant species that utilize spores, instead of flowers or seeds, for reproduction is known as a bryophyte. The non-vascular seedless plants which include mosses, liverworts, and hornworts are classified as bryophytes. There are over 20,000 species of mosses, with some species being microscopic and others reaching heights of over one meter.

They play an important role in ecosystem regulation because they act as a buffer for other plants that live alongside bryophytes and benefit from the water and nutrients they obtain.

Some bryophyte species are among the first to establish themselves on open land. Since many plant species in this community are sensitive to levels of moisture in the atmosphere, which are lower in disturbed environments because there is less shade. The bryophytes are also excellent indicators of habitat quality.

Seeds and flowers are not found in bryophytes. Instead, spores are used to replicate.

Exceptional Features of Bryophytes

A bryophyte's only distinguishing feature is that it lacks true vascular tissue. Some have specialized tissues that transport water, but due to the lack of lignin, they are not considered true vascular tissues.

Bryophytes are thought to have evolved from charophytes and are the first true plants to have appeared on the planet.

Characteristics of Bryophytes

The fact that bryophytes are non-vascular plants is their distinguishing characteristic. Other essential characteristics of bryophytes include:

• Bryophytes are mainly found in moist areas, but they can also be found in a wide range of ecosystems, including deserts, the Arctic, and high elevations. Bryophytes can thrive in conditions where vascular plants cannot because they do not rely on root structures for nutrient uptake (e.g., on the surface of rocks).
• Plants in this group lack roots in favor of crude stems and leaves.
• Instead of roots, they have “rhizoids,” which aid in the plant's anchoring to the surface. The rhizoids do not absorb nutrients in the same way that other plant roots do.
• Mosses release spores from their leaves, which migrate through water and create new mosses.
• Mosses need a lot of water to grow and spread. They will completely dry out and still live. When they come into contact with water, they resurrect and begin to develop.

Classification of Bryophytes

Bryophyta is a division of green plants that includes embryophytes, which are land plants, particularly non-vascular ones. This division consists of the following:

• Mosses – class Bryopsida
• Liverworts – class Marchantiopsida
• Hornworts – class Anthocerotopsida

Plants that are leafy, flowerless, and rootless are known as liverworts. Hornworts are aquatic plants with branched clusters and forked leaflike structures. But for their life cycles, these three plants seem to have little in common. Many mosses are small and live in thick, compact mats, giving the impression that they are one plant rather than thousands. A blanket of soft, spongy moss represents the gametophyte stage of the life cycle of the moss.

The Life Cycle of Bryophytes

All bryophytes possess a dominant gametophyte stage in their life cycles. The plant is haploid at this stage, and the sex organs that produce gametes are developing. The ability of bryophytes to exist in this stage for a long time makes them different from other plant species.

Bryophytes have unbranched sporophytes (the diploid type of the plant) that produce a single spore-producing capsule (sporangium). Furthermore, the sporophytes are nutrition-dependent on the gametophyte and mature inside the female sex organ (archegonia).

The gametophyte or multicellular haploid form taken by a plant during generational alternation is larger and lasts longer than the sporophyte,an organism that develops spores in a multicellular diploid form, in the life cycle of bryophytes. Bryophytes can reproduce both sexually and asexually. Many gametophytes can reproduce without the help of sporophytes. Specific multicellular structures split away from the original plant when this happens. In liverworts and mosses, the tissue clusters detach from the original plant and are transported by water to form new plants. Raindrops or splashes of water from nearby streams may be the source of the water. Small droplets are all that is needed to transport the clusters of cells that will serve as the foundation for new development.

If an organism has two or more distinct types of spores, it is said to be heterosporous. Since they have two types of spores, bryophytes are heterosporous. Male gametophytes grow from one form of spore, while female gametophytes develop from the other. A germinating bryophyte spore starts the normal bryophyte life cycle. The spores begin their development by forming a protonema, which is a mat-like structure. The protonema then matures into the gametophyte stage, where the plant begins to form leaflike structures. The gametophytes form divisions, each of which can be either male or female. The male reproductive organ in mosses and ferns is formed from male spores. The archegonium (plural, archegonia) is a female reproductive organ in mosses and ferns that is formed from female spores and contains the egg. The sperm fertilizes the egg, resulting in the embryonic sporophyte, a simple diploid cell. A foot, a spore capsule, and a stalk are the three structures that the sporophyte develops. The foot anchors the young sporophyte to the gametophyte and acts as a hold-fast. A spore capsule forms at the opposite end of the sporophyte, and the stalk supports the sporangium (plural, sporangia), which is a sac for producing spores. The stalk conducts nutrients to the capsule, where they are used to create spores, while the foot consumes nutrients from the gametophyte. The life cycle begins after the capsule releases spores.

The diploid sporophyte (which has two copies of chromosomes) in bryophytes develops spores that go through meiosis (cell division that reduces the number of chromosomes by half). These spores grow into protonema, which are haploid leafy gametophytes (one copy of chromosomes). Male and female bryophyte gametophytes exist. Fertilization happens when the sperm reaches the egg, and the cells merge their chromosomes to form the diploid zygote that matures into the sporophyte.

Content and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for 

• Bachelors in Biology
• Bachelors in Botany
• Masters in Botany

Related Concepts

• The life cycle of Pteridophytes
• The life cycle of Gymnosperms
• The life cycle of angiosperms