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The Division (family) is made up of Bryophyta (Mosses) Marchantia (Liverworts) and Anthocerotypha .(Hornworts)
The three Divisions have differences but are essentially similar in their biology.
Note:
Club Mosses (Lycopodiopsida) are not part of the Bryophyte family but are vascular plants from the Lycopod plant division, one of the oldest surviving Vascular plant divisions going back over 400 million years. They do reproduce with spores but are altogether different otherwise.
There are two different growth forms for Bryophytes Acrocarpus and Pleurocarpus.
Acrocarpous mosses grow with a single main stem that has no branches growing from it. The plant on the left, Bryum capillare is an Acrocarpus Bryophyte.
Pleurocarpus mosses have a main stem which may have several branches growing from it and these in turn can be branched with offshoots.
The plant on the right has a single main stem with numerous branches growing from it with sideshoots on them. This species is Thamnobryum alopecurum, often referred to as Tree moss for obvious reasons.
This is a Pleurocarpus plant
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Above is a typical shoot from a colony of Bryum capillare (Capillare Thread-moss). This is a very attractive and common moss which can be found in many habitats. You will see from the information arrows the main components which make up this moss. These are the same for all mosses with the exception of shape and size .
Liverworts are somewhat different and described below.
The main body of a Bryophyte in known as the Gametophyte. This includes the main stem, any branches, leaves from the stem and branches, the Rhizoids and depending on what reproductive stage the plant is at, sporophytes.
The image above shows a specimen of the acrocarpus moss Atrichum undulatum. The main features of a leafy moss are shown here. As an acrocarpus species, there is a single main stem with many leaves attached to it, but no branches off that stem.
The leaves on the species are prominently toothed around their margins or edges. This is described as a dentate margin. I don't think the exact reason for the teeth on the margins is known, but they seem to be related to surface area - to allow more moisture to gather - and possibly to allow excess water to run off the leaf easily.
The 'Nerve' also called a 'Costa' runs up the centre of a, in this species right to the leaf tip. Nerves can be quite wide, sometimes very short, and often end at the tip of the leaf. Although called a nerve, it is really a mid rib often more than 1 cell deep.
In many species, the nerve extends beyond the leaf tip and looks like a transparent white hair. The nerve is then described as being 'excurrent' meaning it carries on after the end of the leaf tip. Excurrent nerves can be very short or very long, again depending on the species involved.
Below are several images detailing the various components of Moss Bryophytes. I will include images of Liverwort Bryophytes in the Liverwort reproduction section below
SPORES
The image shows approximately 50 individual mature spores from the species Ptychomtrium polyphyllum (Greater Pincushion Moss)
The spores measure 12.5 µm across.
1µm = 1000th of 1 Millimetre, so they are 12,500th of 1 mm wide.
Imgine these numbering hundreds of thousands.
Moss spores can travel both long and short distances or they can simply fall into or near the the colony they came came from.
Because Bryophytes produce many thousands of spores, many will not develop at all. The high numbers do however ensure that there is a good chance that quite a few will be successful in developing into a new Gametophyte.
The life cycle of Mosses, Liverworts and Hornworts is essentially the same, with spore production and
distribution being achieved in slightly different ways. The spore (reproductive cell) is the 'end product' of the reproduction process. The Gametophyte is the plant produced by a successful spore.
A spore is developed within a sporangia by a plant (Gametophyte) that will itself have originally developed inside a Sporangia capsules or by way of Fragmentation. The newly matured spore is then released into the air and dispersed by water, wind or by being carried on something which moves.
It then falls away from Gametophyte and if it lands on a suitable substrate (surface) in the right environment the spore develops into another gametophyte and the process begins all over again.
The following images show a mass of nearly mature sporangia of the species Ceratodon purpureus(Redshank).
All the capsules are on tall red-stalked seta - hence the common name - and are slightly curved with angled beaks.
The other image us of a large group of wet Polytrichum juniperinum (Juniper Haircap) sporophyte capsules.
When you consider that the above are just two colonies with each capsule containing many thousands of individual spores , it is not so surprising that the seemingly 'haphazard' distribution methods are so successful.
The importance of water
The one thing that very much dictates how well Bryophytes exist and reproduce is water.
In the absence of a vascular system (Xylem and Phloem) of vessels to circulate water throughout the plant, Bryophytes have to absorb water and minerals through their leaves with some help from the Rhizoids at their base. The lack of a vascular system also means the plants cannot grow to be very large. The largest recorded Pleurocarpus Bryophyte in the word is said to be Dawsonia superba. It grows in New Zealand, Australia and New Zealand to a height of 60 cm (just over 23 inches) and its appearance is very similar to our Polytrichum commune, being from the same family.
Other factors assist in channelling the moisture which falls onto plants. Leaves and stems have surfaces designed to channel moisture, leaves often overlap or are 'U' shaped.
The colonies themselves are be very much like dense miniature forests with shade and cooler temperatures assisting in moisture retention. These 'forests' also provide habitats for a multitude of invertebrates.
Success or Failure?
Bryophytes generally reproduce very successfully. Their success depends on a number of factors including the presence or absence of water, ambient temperatures, habitat loss or damage and air quality are but a few.
Some species have evolved and 'specialise' by living in remote and sometimes extremely scarce habitats. These habitats can be so remote and rare that if the habitat is lost the species itself may well become extinct.
Most other species may prefer trees, rocks, stony ground, grassy areas, boggy areas, rivers, streams and ponds, and even former mines where toxic minerals are present. A lot of species can grow in various habitats and even the specialists can sometimes be found in unexpected habitats.
As is often the case with Nature we can be surprised by exceptions to where Bryophytes live and thrive especially when it is different to the norm.
'Typical' habitat can be a big help in finding locations when trying to locate specific species. That doesn't mean you might not find something completely unexpected there.
Other factors assist in channelling the moisture which falls onto plants.
Leaves and stems have surfaces designed to channel moisture, leaves often overlap or are 'U' shaped.
The colonies themselves are be very much like dense miniature forests with shade and cooler temperatures assisting in moisture retention. These 'forests' also provide habitats for a multitude of invertebrates.
Although absorption into the plant via its surfaces is very efficient using capillary action, bryophytes have no means of retaining that moisture. When the ambient temperature rises, the water they contain simply runs out or evaporates into the atmosphere. Hydration and dehydration are continual processes and are linked in the main to lack rainfall and high or low temperatures.
This does not prevent Bryophytes from being very successful.
Their ability to both absorb and lose water is astounding. Place a dried-out moss sample on a flat surface and drip some water onto that surface under the plant. It will immediately ingest the water and change shape, 'inflating' as it takes on the water. The reverse is equally as spectacular. Raise the temperature for the same sample and you will see it begin to dry and shrink until the moisture has gone.
Please note that thalloid Liverworts do not really show this when taking on or losing water. Leafy Liverworts do.
What makes Bryophytes very different from vascular plants is their ability to lose every drop of moisture they have and then to withstand a drought for long periods, recovering completely when rain and moisture returns.
They can also cope with a massive excess of water unlike many vascular plants which cannot.
Flowers and grasses and other plants would simply die in these circumstances unless very deeply-rooted.
It is worth noting that very dry mosses and liverworts look very different from hydrated samples and can be almost unrecognisable for what they are.
Finally, the importance of water cannot be stressed too much when it comes to reproduction.
Water is essential to allow sperm to reach eggs and for gemmae to be washed away from the parent plant to grow elsewhere. It is also essential in providing the right conditions for spores and fragments to grow into new plants.
Click on the image below to view hydration and dehydration in slow motion.
Bryophytes can reproduce sexually and by vegetative fragmentation. Mosses use slightly different methods to Liverworts and Hornworts.
Gametes - the Male sperm (Antheridium) and Female eggs (Archegonium) develop on the Gametophyte - the plant body.
Both rely on water lying or flowing on the Gametophyte to bring them together and allow fertilisation to take place.
A fertilised egg will then produce a Sporophyte (collectively Sporangia) which in turn develops spores inside the urns or capsules which are surmounted by two lids calyptra and cap that retain the developing spores within the capsule.
The capsule itself is supported on a seta or stem which often grows higher than the Gametophyte or plant body. In some species the seta is short and hidden in the foliage of the Gametophyte. The upper end of the seta can often be bent over or 'Swan-necked'. Other capsules have very short seta. The sporophyte is always attached to the Gametophyte.
Spore Dispersal
Once mature, the Calyptra , operculum and lid fall way from the sporophyte exposing the peristome teeth on the annulus ring. The teeth vary considerably from one species to another and once exposed, they extend in different ways to assist the dispersal of the spores themselves.
Once released dispersal very much depends on the weather conditions and habitat. Spores may be blown for short or long distances or may fall on or near to the colony they came from. The actual size of the spores, which varies from one species to another, can also influence how far they are blown.
I understand that the number of spores actually produced varies, but is certainly numbered in millions. The actual life-span of a single spore is not certain, but again will vary with the weather conditions prevalent when they are released.
Reproduction by Fragmentation
All Bryophytes can reproduce by vegetative fragmentation.
This process does not involve the fertilisation of eggs but does result in a new plant being formed. It is very similar to a gardener taking a cutting from one plant and allowing it to grow into a new one.
Vegetative reproduction amongst Bryophytes is said to be more common than reproduction by sporangia.
What parts of a Bryophyte can reproduce using vegetative fragmentation? Any small living fragment. from a Bryophyte has the ability to become a vegetative propagule which, assuming it falls on a suitable habitat, can grow into a new plant.
That fragmentation can occur in Bryophyte and Liverwort colonies is not at all surprising and there are endless ways in which this can happen.
Fragments can occur naturally as a plant grows, disturbance by animals, birds and people, high winds, fast flowing water, falling branches. There are innumerable ways in which a Bryophyte can lose part of its Gametophyte. Not all bryophytes grow on level ground, may grow high up, others on trees, many near running water. Those in or on trees can be dislodged and damaged and so on. Sporangia falling away from the parent plant can also result in fragments.
What is perhaps surprising is that colonies can expand and grow in size as a result of Vegetative Fragmentation and propagules alone.
At the outset I have to confess that I have yet to actually see a Hornwort in the field.
As their name implies, they produce an erect horn-like growth which is the Hornwort equivalent of a Sporophyte. The Gametophyte of a Hornwort is flattened in a similar way to thalloid Liverworts. As you read on, you will see how many Liverworts and Hornworts differ from mosses in both appearance and how they reproduce.
The methods still use the same principles as mosses and they do produce sporophytes, propagules and spores, they just look different. The image below demonstrates this in a Thalloid Liverwort.
Lunularia cruciata (Crescent-cup Liverwort) is a thalloid liverwort with leaves which are flatter and thicker than those of Leafy Liverworts which more closely resemble mosses.
Below, you can see the semi-circular cup containing Gemmae and beneath that the leaves with their air pores and distinctively shaped cell patterns.
In contrast to the Thalloid Lunularia cruciata, below is an image of the leafy liverwort Jamesoniella autumnalis (Autumn Flapwort).
This specimen is in a reproductive state with developing sporangia arrowed lower right.
As you see, it resembles a leafy Moss and does not have the 'rubbery' appearance of the thalloid specimen above.
NOTE: You will notice that the common names of Liverworts often have 'wort' in them as does Liverwort. My understand is that 'Wort' is derived from the Old English word WYRT, meaning plant, herb or root.
Liverworts can form deciduous branches and some species produce leaves which are completely deciduous or have weak lines which allow parts of the leaf to break off easily.
Leafy Liverworts produce leaves that are lobed or long and narrow like fingers. Mosses too can produce deciduous leaves. The parts that fall away are all capable of producing new plants by way of vegetative propagules.
The endogenous female pseudoperianth is growing within the leaf cells and will emerge as it develops.
Upper right in the image are the male Antheridia the sperm of which will have washed down over the Female pseudoperianth to fertilise the eggs within.
The image below shows a specimen of Marchantia polymorpha subsp. Ruderalis (Common Liverwort), also a Thalloid liverwort which develops exogenously or on the surface of the plant's gametophyte. This is a very distinctive species with the female Archegonium resembling small palm trees.
Below is another image of Marchantia polymorpha showing the Gemmae cups containing Gemmae. Water will wash these Gemmae out of the cups and if they reach a suitable substrate, they will then produce new plants.
This species grows on my block-paved driveway and recently reproduced so successfully that nearly half of the drive was covered in new plants.
Below is an image detailing the various components of Jamesoniella autumnalis (Autumn flapwort).
This specimen was collected from the branch of a tree growing on the edge of the bank of the River Nant, Glen Nant, Lorn, Scotland. It was growing amongst other Liverworts.
To emphasise again how tough and hardy these plants are, when I collected the specimen there was not much evidence of it being in a reproductive state. It was damp when I placed in an envelope.
Removing it to examine and dry it out over a week later, it was happily producing the sporangia from several shoots as you can see below.
This is a liverwort that reproduces in the same way as mosses with sporophytes developing from the stem of the plant and producing spore-laden capsules.
In addition to the reproductive methods detailed here, mosses can also produce Rhizoidal Gemmae (Tubers) attached to the plant's Rhizoids. Being external to the plant, these are exogenous growths.
This type of Rhizoidal Gemmae do not appear on Liverworts or Hornworts. Instead, they form swellings at the apices of shoots or lobes (also referred to as Tubers) which turn towards the earth and form below ground level - see image below. In both Mosses, Liverworts and Hornworts it is thought that the Rhizoidal Gemmae and Liverwort Tubers, growing as they do below ground level are a means of survival for the plant itself.
Above is an image of the leaves of the thalloid liverwort Conocephalum salebrosum - Great Scented Liverwort - Growing on the shade on the side of a stone bridge in Staffordshire.
The dark brown objects you can see in the lobe notches are actually leaf scales grown to protect buds developing below them. The buds eventually turn towards the substrate and develop into new plants. Another example of vegetative reproduction.
Conclusion
If you are familar with everything in this section, you can then use that knowledge as another tool to assist you in getting to know Byrophytes and to identify them.
It is fairly obvious that the reproductive methods which at first looked wasteful and haphazard actually result in the tremendous success of Bryophytes.
You will see most of the living components described above as you journey into the world of Bryophytes. I hope you enjoy that journey!