Common Name :
Bryophytes are very common, even in urban areas and many people have seen them, many people call them “mosses or lichens”. Bryophytes like ferns hold a special place in my heart. I do not claim to be an expert but my love of bryophytes and ferns have led me to a new miniature world of shear beauty beyond comprehension. A single rock or log may contain thousands or millions of individual plants.
You don’t need to know anything about bryophytes to understand their environment or what their names are. To enjoy the bountiful variations in a single community is enough justification to begin your trek of not a thousand kilometers but just a few meters to discover this all new exciting world. The best starting point for someone who knows nothing about bryophytes is to ask “What are Bryophytes?
The word bryophyte is the collective term for mosses, hornworts and liverworts and bryology is the study of bryophytes. While they are all closely related there are marked differences between the three. So a moss is a bryophyte, a liverwort is a bryophyte and a hornwort is a bryophyte.
Not all the mossy looking things you see are mosses.
There are various small, green organisms that are not mosses. However, leafy liverworts are obviously very similar to mosses, since they both have leaves on stems.
All bryophytes contain chlorophyll and so make their own food from water and carbon dioxide, via photosynthesis with the exception of one liverwort Cryptothalluswhich lacks chlorophyll and relies on a symbiotic relationship a fungal partner for food.
Bryophytes vary in size from plants 1mm to 100mm in height by 2mm to 1000mm in diameter. A common misconception is that bryophytes are found in cool, humid, shaded stream rainforest localities. The fact is bryophytes can be found throughout the year in areas ranging from arid localities to tropical and temperate rainforest. They prefer relatively unpolluted areas.
Bryophytes don’t have true roots. They have rhizoids which act as anchors or stabilizers for the plants rather than to extract food from the soil, rocks or logs they are growing on.
They are produce spore like ferns and fungi. Bryophytes are best studied with a hand lens 10 power and photographed with a 1:1 macro lens and a tripod.
Bryophytes quickly absorb and retain many times their dry weight in water especially when it rains. They also absorb nutrients from the air. An extensive bryophyte mat or curtain; in the case of epiphytic Bryophytes have large surface area. This large surface area is very efficient at absorption.
Try adding a single drop of water to a mat of dry Bryophytes and watch the water move through the mat. Use a 10 power hand lens for better results.
Reproduction & Spore Dispersal: Basically Bryophytes reproduce both sexually and asexually. The spore capsules are produced after a male gamete or sperm has fertilized a female gamete or the egg. Hence the spores are part of the sexual reproductive cycle. In the majority of the bryophytes spore dispersal is by wind.
The gametes are produced on what’s called the gametophyte and the spore capsule is called the sporophyte and this grows from the gametophyte. In mosses and leafy liverworts the stems and leaves make up the gametophyte. In hornworts and thallose liverworts the gametophyte is the flattish sheet.
Gametophyte: Is the leaf like structure often processing roots of a moss, liverwort or Hornwort which are responsible for the fertilization of the female egg before developing into a sporophyte.
Sporophyte: Is the reproductive capsules of plants that contain spore. Ferns, Club Mosses, moss, Liverwort or Hornwort etc.
Bryophytes can reproduce asexually in several ways. Simple fragmentation is one method where a section breaks off and lands in a conducive, habitat, it can grow into a new plant.
Many bryophytes produce what are called gemmae. Each gemma is a small aggregation of cells, capable of growing into a new plant. The gemmae may be produced in specialized structures, as tiny out growths from some part of the gametophyte or simply loose on the gametophyte.
How do Bryophytes differ from ferns? Ferns produce spores. Ferns have well developed internal conducting systems that carry nutrients from the roots to the leaves of the plants. Flowering plants also have advanced conducting systems. Ferns are intermediate between bryophytes and flowering plants, since they show some features of each.
All plants have gametophytes and sporophytes, but there is a considerable difference between the major plant groups as to which is the dominant stage. In the bryophytes the gametophyte is dominant. Gametophytes are persistent and, from time to time, give rise to sporophytes. Spores produced by the sporophyte germinate to produce more gametophytes, which may then give rise to more sprophytes and so on. We speak of an alternation of generations, between the gametophyte and sporophyte phases. In the flowering plants the sporophyte is the dominant phase with the gametophyte reduced to just a few cells. Roughly speaking, ferns are in between.
According to the Australian Herbarium Australia is not well represented in Bryophtyes as the following chart shows. In saying this, the knowledge of Bryophytes in Australia is really in its infancy.
|World||8,000 – 10,000||4,500 – 5,000||100 – 150|
Some species are very effective sand and soil binders and can help in dune stabilization and erosion control. In arid areas bryophytes, in association with lichens, can create extensive crusts on the soil and such crusts help maintain the underlying soil structure by cutting down evaporation but allow excess moisture to absorb through to the soil.
Bryophytes are often the first plants to colonize barren surfaces like road cuttings, rocky outcrops, volcanic ash and abandon farm land and pastures.
In fact Bryophytes are the cockroaches of the plant world when all else has vanished into extinction it maybe the humble Bryophytes that remains.
The mosses leaves grow from stems with a solid usually erect stalk topped with a capsule where the spores are located. The stems are usually shorter than those found on Liverworts. The mosses in the families Dawsoniaceae and Polytrichaceae provide striking exceptions to the general rule stated at the beginning of the previous paragraph. Within these families the stems are fairly firm, with the plants being upright and quite robust, however they contain no lignin and are not woody like flowering plants. In some species the spore capsule may be stalkless.
There are essentially two growth forms for moss plants mat and trailing. In mat forms the stems are basically erect, with just one upright stem per plant or with the initial erect stem producing some branches, depending on the species, giving the individual plant like miniature forests.
In the other growth form the mosses are a creeping plants usually hanging similar to curtains from branches of trees. The trailing mosses are more highly branched with the branches growing along the substrate or in many specie also producing short, upright branchlets. Branches develop from surface cells in the originating stem and in most mosses branches are simple, single outgrowths from the originating stems.
If there is only a very rudimentary stem the plant will look like a bunch of leaves growing from just a single point. In genera like the Polytrichum and Dawsonia the individual plants are typically just single stems, with branching rare. Amongst the upright mosses there are the so-called “dendroid” mosses, which have several branches appearing from the apical section of the stem.
There are many erect stemmed species of moss where the plants grow very close together in mats or cushion colonies. In such cases it can be difficult or even impossible to make out the individual plants, unless you carefully tease apart a small section of the mat or cushion to see it is growing
In the case of the cushion like growth, much of the cushion may be composed of past generations forming a peaty layer beneath with a green mass overlying the dead material. The peat section is mixed with other organic matter that may have been trapped by the plants making up the mossy cushion. You will see the leaves, stems and sporophytes in the peaty layer. As the stems continue to grow, more and more dead material accumulates below. Such largely dead cushions are more characteristic of moist areas, where they can grow to a considerable size.
A good example is often found in the various Sphagnum moss specie. The branches develop in fascicles. Within such a fascicle, some of the branches will be stout and spreading, while others are slender and drooping.
Simple stemmed species grow separately from each other. They look like dwarf, green pine trees poking up from the soil.
In a creeping moss there may be short, leafy branches that grow away from the substrate but such branches are simply off-shoots from the creeping stems. There are also moss species that produce long, trailing stems but where apart from a small attachment area the stems don’t cling to anything. In such cases you can see a pendulous, curtain-like growth, such as that of Papillaria flavolimbata.
Moss Sporophytes: The sporophyte consists of a spore-containing capsule which is often attached to apex of a stem called the seta.
In almost all moss species the capsule has a well defined mouth opposite the stem or the point attaching the capsule to the stem. When there is a mouth, the spores are released through that mouth called a poricidal. There are very few mosses without poricidal the genus Andreaea is the only native one I know. It is commonly found in polar districts, alpine and sub alpine. The capsules of Andreaea do not have mouths but instead have transversal slits in the sides of the capsules. In some genera like Archidium the capsules rupture irregularly. Moss spore capsules do not have elaters or pseudo elators.
The mature spore capsules are erect, held at any angle or are inverted.
Hornworts are more like a single leaf. The main part of the plant consists of a blue-green to greenish, flat surface usually appressed against the surface it is growing on. They may be lobed and are often crisped on the margins. This flat surface is known a thallose growth habit. In hornworts the spore capsules are thin, tapering horns or needles that grow out from the thallose.
You might sometimes confuse hornworts with thallose liverworts which also have sheet like gametophytes. The hornworts constitute the smallest group with in the Bryophytes. There are six generally accepted
genera: Anthoceros, Dendroceros, Folioceros, Megaceros, Notothylas and Phaeoceros. The name is derived from the Greek word keros which means “horn”.
As noted above, the hornwort gametophyte is an often lobed or crisped, strap like, branched or rosette. The thallus is usually deep green, pale green or yellow-green in Notothylas and is usually many cells thick with the exception of Dendroceros.
Dendroceros’s thallus is strap like; branching several times with each strap having a thick, central midrib with thin singular cellar crisped lateral wings. There’s more about thallus growth in the LIFE CYCLE section.
Hornwort thallus usually have 1 large chloroplast cell or up to 12 chloroplasts per cell in the genus Megaceros. Mosses and Liverworts never have a single chloroplast having numerous chloroplasts per cell.
The Hornwort Sporophyte: A single thallus produces many sporophytes and a hornwort sporophyte is typically an erect, elongated, tapering, horn or needle structure. The sporophytes measure 20mm to 110mm in length though in the Notothylas genus the sporophytes are very small, often less than 5mm in length and lie roughly parallel with the thallus or angle slightly upwards. Regardless of the shape, the entire structure is a spore capsule. The sporophyte is sessile where as they are usually stalked with mosses and liverworts.
The sporophyte except in the genus Notothylas is constantly growing from a point just above its base. As new cells develop there, the apex on the sporophyte is naturally pushed up and out. In theory this process of cell addition and sporophyte growth could continue indefinitely only if it were not for environmental interferences like the weather, soil nutrient herbivores or being overgrown etc. If the gametophyte suffers in anyway the sporophyte growth stops.
The youngest cells are near the base with the oldest cells at the top which is in reverse to most plants that grow at the apex of their cells that is the root apexes or leaf apexes. The spores mature within the growing sporophyte and the first to mature the spores at the top. The spores at the bottom will mature last. The sporophytes split longitudinally starting from the apex to release the spores over an extended period. The sporophytes often split along two lines opposite one another. Within each capsule; of most species, there are elators as well as spore. Elators are microscopic, spiral like structures which usually twist or untwist in response to changes in humidity. This helps in the spore ejection from the capsules.
Liverworts are the problem children because they have 2 growth forms similar to the thallose species and leafy species with the latter having leaves on stems, just like mosses. The stems are usually much longer compared to those on mosses. The spore capsules are produced in various ways. In the thallose Liverwort genus Riccia the capsules are embedded in the thallose sheet as can be seen in the photograph to the left. Note the empty cavities near the base of the thallose. Those are spore capsules which have opened and from which most of the spores have been dispersed. In leafy liverworts and a number of thallose Liverworts the capsules are positioned at the apex of the stalks.
Many people are familiar with the thallose on the liverwort species Lunularia cruciata. It can form large colonies in glasshouses and in flower pots. However, while a few of the thallose liverwort species are quite conspicuous, there are far more leafy species than there are thallose species of Liverworts.
That is there are more simple thallose species than the complex thallose species which are far less robust and are therefore easily overlooked.
Leafy Liverworts are easily confused with mosses which also have a leaves on stems form.
The gametophyte is the dominant stage in terms of both bulk and longevity. All liverworts produce mucilage, which helps liverworts absorb and retain water. The mucilage is produced by the gametophytes, either internally in special cells known as slime cells or externally in papillae specially modified to produce the mucilage.
Since liverworts are photosynthesizing plants, their cells contain chloroplasts. In addition to chloroplasts, the cells of most liverwort specie contain oil vacuoles. These vary in size, shape and number per cell, depending on species and are useful in identification of the different species. The oil is usually colourless though brown and blue are known found. The oil bodies in some specie are found in the majority of cells, while in other specie they are confined to isolated cells. The oils are various forms of terpenoid compounds. The oils often give the Liverworts a distinctive aroma or taste.
Liverworts lack roots but anchoring rhizoids are present. Most the rhizoids are single cellular.
The male and female gametes; sperm and eggs are produced on the gametophyte with a fertilized egg developing into a spore bearing sporophyte.
The sporophytes: The Liverwort sporophytes may develop in a variety of ways, which cannot be summarized simply and need to be dealt with when looking at the different types of liverworts. There are some common features.
* They all produce a capsule for the spore.
* The spherical to cylindrical capsules are blackish when mature.
* The mature capsules spilt open to release the spores. Within each capsule; of most species, there are elaters as well as spore. Elators are microscopic, spiral like structures which usually twist or untwist in response to changes in humidity. This helps in the spore ejection from the capsules.
In the leafy liverworts the sporophyte consists of a spore capsule at the apex of the seta. The seta is attached to a stem of the gametophyte.
In thallose liverworts the sporophyte may appear in various ways, including the same capsule on a seta similar in form to those found on leafy liverworts. In some genera the spore capsules appear on quite complex supporting structures. In the genus Marchantia the spore capsules are formed on the undersides of an umbel comprising several leaf like thalli. The umbel and the basal, green thallus it grew from are both gametophytes. The sporophytes are usually hidden within cream, yellow or golden floccose remains of spore and elators. The stem holding up the umbel is not a seta.
Water and Bryophytes: Many bryophytes are able to survive extended periods of extreme dryness or extreme cold by remaining dormant and adapting various survival mechanisms. Many moss species in such areas grow cushion like with each cushion being a dense colony of individual plants. In this way most of the colony is protected from the direct effect of the harsh conditions. Many arid area bryophytes curl up in various ways to reduce their exposed surface areas. In various species the chlorophyll undergoes a change in structure in order to survive the dry periods undamaged. You’ll find natural anti-freeze in various cold-area bryophytes.
Dormant bryophytes are able to extract moisture from fog or dew. This is why you can find bryophytes in deserts where rainfall may be very rare. They are able to then photosynthesize for a few hours before the heat of the day when they return to the dormant state.
Most bryophytes absorb water and dissolved minerals over their entire surface, through the leaf surfaces or stems. This means the absorbed water and minerals are immediately available to start the process of photosynthesis.
Many bryophytes have various structural features which assist in water conduction with overlapping leaves on stems, rhizoids with matted hairs, leaves that are ridged or with tiny warts or scales on the underside of a thallose bryophyte may help water move along the plant by capillary action and dead leaves and thallose often act like sponges storing water for later use.
In a number of bryophytes water is also conducted internally in fairly rudimentary conductive tissue. Some mosses in the families Polytrichaceae and Dawsoniaceae the stem conductive tissues are well developed but not to the extent which is found in flowering plants.
Many people blame Bryophytes for killing their lawns especially the mosses and Liverworts. Mosses or liverworts can grow in a lawn but they definitely do not kill grasses. In fact in a healthy piece of ground Bryophytes will eventually succumb to the pressures of lawns and grasses. The question is raised if you have bryophytes growing in your lawn it is probably because you have created conditions better suited for bryophyte growth than for lawn growth. For example, the lawn around the base of a well-established tree is often patchy to non existent but it may be better suited for growing Bryophytes. The tree may cast shade not suitable for sun loving specie of grasses. It may reduce the moisture in the soil making it harder for lawns to survive or the soil due to poor organic management is devoid of carbon which Bryophytes like and grasses struggle in. Perhaps the area of poor lawn is one where drainage is poor, so that the soil becomes too waterlogged for good lawn growth but ideal for various bryophytes. The poor drainage, not the bryophytes is causing the death of the lawn not the Bryophytes. Bryophytes and lawns can co-exist. So instead of blaming the poor bryophytes’ maybe we should first look at our own gardening practices.
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