Bryophytes include the mosses (Musci) and liverworts (Hepaticae). These are undoubtedly plants but they lack features of higher plants like vascular tissue. Mosses are concidered by many as posessing leaves and stems while liverworts are thought of as flattened and thalloid (liver-like) in shape but actually there are far more leafy liverworts than there are mosses.
Moss is a term applied wrongly to many plants including ‘Sspanish moss’ which is really a higher plant from of the Bromeliacae line.
The evolution of bryophytes remain under speculation and they cannot clearly be linked to other plant groups. Thus, they form their own very inique forms and plant group within the plant kingdom.
The bryophyte life cycle is unique to the group in that they have two alternating generations, both different yet similar to each other. First a haploid spore germinates and creates a filamentous or oval shaped stage which is often plate-like in appearance. This precedes the formation of leafy shoots or gametophores. These are often green and exist for several months or even years (think fairy rings). This stage bears the sex organs the antheridia and the archegonia.
In bryophytes a distinguishing features of their life-cycle is that at this stage a male gamete which is highly mobile is produced and travels to the female sex organ, usually in water, to fertilise the egg. A zygote is formed and then the next generation – the sporophyte – grows. This is the one which produces the spores and can be observed in moss forms as tiny, taller stalks on top of which are little black dot-like spore producing organs.
Different methods may be used to distribute the spores from which new gametophores will eventually grow. It is because of the production of these stalks and their green appearance that many try to link bryophytes, especially mosses , with other plants but their internal structure, life cycle and other features make them stand out as a very separate group.
They have to be small because their method of reproduction is limiting and is only successful in tiny plants (relatively). The largest bryophyte only ever reached around 60cm in height.
Bryophytes have proved a real problem for botanists to classify and so far have only been put into 2 classes and 8 orders – a very small amount of groups for classification but this may change.
Bryophytes play a huge role in the establishment of plant communities because they have the ability to colonise almost bare rock faces, existng in the minutest of crevices and turning what was barren rock into productive material. Their waste and rotted matter will eventually form the soil upon which seeds of small pioneer plants may germinate. These in turn produce waste, push roots into the rock and further develop the soil and eventually you get larger plants, animals and communities yet if it were not for the liverworts and mosses, there would have been no starting point and erosion would simply have created sand or crumbled rock.
So, bryophytes, along with a few other plants considered ‘primitive’ like algae and lichens actually prove themselves to be incredibly valuable building blocks in plant communities ever reaching their full potential.
They are also important in recycling nutrients and changing the chemistry of an area to be ably to support higher plants because they can withstand and tolerate conditions which would normally be unsuitable for larger plants.
So, the greening of many places is started not by your magnifcent ferns and trees but by the ever-so humble, yet massively important bryophytes.
Next time you are out, look closely at the rocks at your feet – you may see some of the most important members of the plant community.