The Bryophytes are a division of plants that includes all non-vascular, land plants and can be split into three groups: mosses, hornworts and liverworts. Although each group is genetically very different they each share some common adaptations which have led to them currently being clumped together as Bryophytes.
In addition to being non-vascular, Bryophytes have a set of common features that help to distinguish them from all other land plants. Mosses, hornworts and liverworts all reproduce using spores rather than seeds and don’t produce wood, fruit or flowers. Their life-cycle is dominated by a gametophyte generation which provides support and nutrients for the spore producing growth form known as the sporophyte.
Some Bryophyte species have evolved special tissue which allows them to transport water and other substances through their tissue. However, the tissue doesn’t contain lignin, an essential protein found in true vascular tissue. This specialized tissue is therefore not considered to be vascular tissue although it does a respectable job of performing a similar function.
Where are Bryophytes found?
Bryophytes can be found in wet environments all around the world. Because they have no vascular tissue, they aren’t able to take water from the soil and transport it to higher tissue.
Bryophytes need wet and often well shaded environments which deliver a lot of rain water for them to soak up. Bryophytes are therefore common on the forest floor and tree stems in rain forests, wetland ecosystems and at high altitudes. They also find their way into urban life by establishing on places such as bricks and in the cracks of paved surfaces.
How old are Bryophytes?
Bryophytes are the oldest of all land plants and are believed to be the closest remaining link between land and aquatic plants. Their soft tissue makes fossil records bleak but the oldest evidence that has so far been found can be dated back to almost 500 million years ago.
Spore-like structures of a liverwort were found in Argentinian rock dated to 473-471 million years old. The first evidence of mosses appear much more recently between fossils aged between 299-250 million years old. Due to the poor preservation of Bryophyte species, it is quite possible that the Bryophytes are significantly older.
How did Bryophytes evolve?
It is believed that the division Bryophyte evolved from green algae on more than one occasion. Genetic analysis has shown that Bryophyte species do not share the same common ancestor and in some cases they are only distantly related.
Two adaptations made the move from water to land possible for Bryophytes: a waxy cuticle and gametangia. The waxy cuticle helped to protect the plants tissue from drying out and the gametangia provided further protection against drying out specifically for the plants gametes. Bryophytes also show embryonic development which is a significant adaptation that links them to the vascular land plants.
How big are Bryophytes?
Bryophytes are all pretty small plants as they are limited in size by poor transport methods for water, gases and other compounds. Even the largest moss can only grow as tall as 50cm but much larger colonies of bryophytes can often be found. These colonies are made up of many smaller individuals that work together to absorb and retain water.
How does their life-cycle work?
Like all land plants, bryophytes have the have a life-cycle that alternates with each generation. One generation is known as the gametophyte and the second is the sporophyte.
The gametophyte produces haploid spores with only have the genetic material of gametophyte cells. The sporophyte is grown when released spores germinate in a new environment and begin dividing. For bryophytes, the gametophyte is the most obvious generation. The sporophyte is usually very small and dependent on the gametophyte for support and nutrients.
The following sporophyte generation occurs when a sperm from one gametophyte fertilizes an egg from another gametophyte. Fertilization is only possible when gametophytes are covered with a thin layer of water which can allow the sperm to travel through towards a neighboring gametophyte.
Why are Bryophytes important?
Bryophytes are a critical link between aquatic and land plants and they contain a number of adaptations that are characteristic of both land and aquatic plants. As mentioned above they have cuticles, gametangia and embryonic development which are all features of more advanced, land plants. On the other hand, they still require water for reproduction and lack vascular tissue. This linkage is vital in piecing together the evolutionary history of life on Earth.
Besides that, Bryophytes provide a number of important services that help maintain the integrity of a landscape. They are important for their role in water filtration, primary production and provision of habitat for insects and other invertebrates. They have also been utilized by humans for a number of purposes both historically and in the present day. Traditionally, they have been used for insulation, padding and as a fuel; more recently they are mostly used in the florist trade.
Last edited: 18 May 2015