Bryophytes Habitats and Distribution

Study Notes

Bryophytes can be found in various habitats, including tropical, temperate, and arctic regions, with high moisture conditions.
Some bryophytes are xerophytic, growing in desert conditions with typically dry conditions.
Few bryophytes are truly aquatic, with underwater forms, such as Riccia fluitans.
Bryophytes can be found at elevations ranging from sea level to over 18,000 feet above sea level on mountains.

The plant body of bryophytes is thallus-like and more differentiated than that of algae.
The thallus size can measure up to 1-2 centimeters in height and may be prostrate or erect, attached to the substratum by unicellular or multicellular rhizoids.

Bryophytes are a collective term for three distinct divisions of non-vascular plants: mosses (Division Bryophyta), liverworts (Division Hepatophyta), and hornworts (Division Anthocerotophyta).
There are approximately 23,000 different species of bryophytes, lacking true xylem or phloem.
Liverworts, mosses, and hornworts have distinct characteristics, such as:
- Mosses: have water-conducting cells called hydroids and food-conducting cells called leptoids, anchored by filamentous multicellular rhizoids.
- Liverworts: have flattened, lobed, somewhat leaf-like bodies (e.g., Marchantia sp.), and grow prostrate rather than upright.
- Hornworts: have chloroplasts in each cell, pores and cavities filled with mucilage, and are often rosette-like in form.

Bryophytes have adapted to land environments through:
- Possessing root-like rhizoids to absorb water from the soil.
- Having a water-proof waxy coating on the surface of the epidermis to prevent water loss.
- Possessing stomata-like structures for gaseous exchange.
- Possessing multicellular sex organs surrounded by sterile jackets to protect them from drying out.

Bryophytes require an external source of water (rain or dew) to reproduce.
Alternation of generations is a characteristic feature of their life cycle, with the gametophyte being the conspicuous and dominant generation.
In all bryophytes, the sporophytes are permanently attached to the gametophytes, varying in their dependence on them.

The gametophytic generation is the more conspicuous phase in the life cycle, being long-lived and dominant.
It is independent, green, fleshy, and autotrophic.
Gametophytic plant bodies consist of parenchymatous cells only, lacking thick-walled and lignified cells.

The sporophytic generation is the less conspicuous phase, being short-lived and completely nutritionally dependent on the gametophyte.
The sporophyte develops from the embryo and is the first stage in the diploid sporophytic generation.
The sporophyte is differentiated into foot, seta, and capsule.

Reproduction is generally by vegetative and sexual means.
Vegetative reproduction includes:
- Fragmentation of thallus.
- Production of gemmae in gemmae cups (in liverworts).
Sexual reproduction is oogamous, with multicellular sex organs and a dependent sporophyte generation.

Sexual reproduction involves:
- Antheridia (male sex organs): stalked and globose, with one cell thick sterile jacket, producing biflagellate antherozoids.
- Archegonia (female sex organs): flask-shaped, with one cell thick sterile jacket, containing egg cells.
Fertilization requires water, with antherozoids attracted by chemicals in the mucilage and fusing with egg cells to form a diploid zygote.