Bryophytes: mosses and liverworts
 
Collectively called Bryophytes (the Greek bryon is a tree moss or oyster-green, phyton is a plant), mosses and liverworts are ancient plants dating back almost 500 million years – way before the dinosaurs, in what geologists call the Ordovician Period when the first sea urchins were developing in the seas, some of the older volcanic rocks of the Lake District and Wales were erupting and the Skiddaw slates were being deposited. 
 
Mosses and liverworts are found only on land and in freshwater, and are unique among complex land plants in lacking the lignified vascular tissue that all ferns, conifers and broad-leaved plants (collectively called "higher plants") have. For this reason they can't conduct large amounts or water or sugar solution up and down their stems, so can't grow very tall.  Many can survive long periods of drought, and rehydrate and start to grow again when properly wetted.  Bryophytes reproduce and disperse through tiny spores rather than seeds,  and also vegetatively by fragmenting, and by special structures called gemmae.
 
Life cycle
Like ferns, bryophytes have two life stages, which differ in the number of chromosomes In their cells. In “higher” plants and most animals, the dominant or main life stage is diploid – with two copies of each chromosome, one from its female and one from its male parent. A haploid cell or organism has only a single set of chromosomes.  To reproduce sexually, diploid organisms first need to halve the chromosome count, producing haploid eggs and sperm. When these come together and fuse, the diploid chromosome count is restored and an embryo can form.
 
In mosses and liverworts by contrast, the dominant life stage is the haploid phase called the gametophyte, because it produces gametes - eggs and swimming sperm.  Fertilised eggs grow into the diploid or sporophyte stage which is small and remains attached to the parent female gametophyte.  It is confined to producing the next generation of haploid spores. When these germinate they grow into the next haploid gametophytes.  The structure containing the spores is called a sporangium (plural sporangia), often held on a slender upright ‘stalk’ called a seta, which allows the minute  spores to be released above the ground making for better dispersal.
 
This two-stage life cycle is sometimes call "Alternation of Generations" In some algae both life stages are equally prominent.  In the ferns it is the sporophyte, in the bryophytes the gametophyte, and the sporophyte is usually very small and inconspicuous.
 
 
 
 
 
 
 
Bryophytes also reproduce asexually, producing "gemmae"which are asexual cells or groups of cells, often produced in specialised little cups, that can detach and form a new plant. Think of these as the equivalent of a gardener taking some cuttings. More haphazardly, any bit of broken bryophyte falling onto the right sort of ground conditions can grow into a new plant – good job they are small or they could take over our gardens.
 
Gemmae developing in cup-like structures on the liverwort Marchantia polymorpha 
Moss or liverwort?
 
The two groups are quite easily distinguished.  If there is no clear differentiation into leaves and stems, and the plant body is segmented or lobed, it is a thalloid liverwort. If it has a stem with leaves in ranks arranged laterally (sometimes with three ranks of leaves, the third smaller and under the stem), it's a leafy liverwort. There is more about liverworts on our page here.
 
        Typical thalloid liverwort Conocephalum conicum                 Leafy liverwort Plagiochila porelloides
 
Mosses all have differentiated stems and leaves, and the leaves are not usually arranged strictly in ranks, and generally surround the stem, leaves are small, and can be rather like scales. They can form neat cushions, often with prominent sporophytes, or appear as straggly bunches. We show something of the variety of mosses on our page here.
    Typical mosses  Grimmia pulvinata                                  Brachythecium rutabulum 
 
Hornworts
Purely for completeness, we mention another bryophyte group, the hornworts (not to be confused with the pond plants of the same name). Hornworts form a small group, with only four species in Britain and Ireland, and of these, field hornwort Anthoceros agrestis is the most widely distributed.  They are not uncommon in damp stubble fields and woodland margins, and probably could occur in rural gardens.  Hornworts have uniquely algal-like features as well as other features more like vascular plants.1.  The gametophyte is the main life stage and rather like a thalloid liverwort, but the sporophytes (the horns) are large and green and self-sufficient.
 
Studying bryophytes
 
Even though bryophytes are common everywhere, indeed, appearing on all continents including Antarctica, they are often ignored – possibly owing to their small size, lack of familiar features like flowers,or the difficulty of identifying them when they are dried up and shrivelled in droughted conditions. But they are really beautiful if you take the time to look.
 
They grow everywhere and anywhere – on tree trunks and branches, in lawns and meadows, in woods, in water, on roofs, on gates and walls, on paving stones, in the little gaps between surfaces and on soils. There is an enormous diversity of shape, colour, and structure. Many have their own fungal associates; others are full of little invertebrates like springtails and mites. They are a home to a myriad animals. They protect your soil from drying out and happily contribute more carbon to your soils’ organic matter because they grow slowly. So get out your hand lens, magnifying glass or microscope, collect little samples, put into a thin film of water so they can rehydrate and then have a close look under a good table lamp.
 
 
References
 
1.  Li,F-W, et al (2020) Anthoceros genomes illuminate the origin of land plants and the unique biology of hornworts.  Nature Plants 6:259–272  Available here.
 
Finding out more
 
Books
Atherton, I.,Bosanquet, S. and Lawley, M.  (2010).  Mosses and liverworts of Britain and Ireland: a field guide. British Bryological Society
Field Studies Council  Garden mosses guide
Porley, R. and Hodgetts, N. 2005 Mosses and Liverworts Collins New Naturalist Library (97)
 
Websites
Bryophytes website (UK)
Bryophyte identification guidance 
British Bryological Society website   
Bryophytes of Britain and Ireland Facebook Group 
 
Page written by Penny Anderson, compiled by Steve Head
Field hornwort Anthoceros agrestis
 
There is just a chance you might find this in a damp area of your garden.
Bryophytes: mosses and liverworts
 
Collectively called Bryophytes (the Greek bryon is a tree moss or oyster-green, phyton is a plant), mosses and liverworts are ancient plants dating back almost 500 million years – way before the dinosaurs, in what geologists call the Ordovician Period when the first sea urchins were developing in the seas, some of the older volcanic rocks of the Lake District and Wales were erupting and the Skiddaw slates were being deposited. 
 
Mosses and liverworts are found only on land, and are unique in lacking the lignified vascular tissue that all ferns, conifers and broad-leaved plants (collectively called "higher plants") have.  Like ferns they reproduce and disperse through tiny spores rather than seeds,  and also vegetatively by fragmenting, and special structures called gemmae.
 
Life cycle
Like ferns, bryophytes have two life stages, which differ in the number of chromosomes In their cells. In “higher” plants and most animals, the dominant or main life stage is diploid – with two copies of each chromosome, one from its female and one from its male parent. A haploid cell or organism has only a single set of chromosomes.  To reproduce sexually, diploid organisms first need to halve the chromosome count, producing haploid eggs and sperm. When these come together and fuse, the diploid chromosome count is restored and an embryo can form.
 
In mosses and liverworts by contrast, the dominant life stage is the haploid phase called the gametophyte, because it produces gametes - eggs and swimming sperm.  Fertilised eggs grow into the diploid or sporophyte stage which is small and remains attached to the parent female gametophyte.  It is confined to producing the next generation of haploid spores. When these germinate they grow into the next haploid gametophytes.  The structure containing the spores is called a sporangium (plural sporangia), often held on a slender upright ‘stalk’ called a seta, which allows the minute  spores to be released above the ground making for better dispersal.
 
This two-stage life cycle is sometimes call "Alternation of Generations" In some algae both life stages are equally prominent.  In the ferns it is the sporophyte, in the bryophytes the gametophyte.
 
 
 
 
 
 
 
Bryophytes: mosses and liverworts
 
Collectively called Bryophytes (the Greek bryon is a tree moss or oyster-green, phyton is a plant), mosses and liverworts are ancient plants dating back almost 500 million years – way before the dinosaurs, in what geologists call the Ordovician Period when the first sea urchins were developing in the seas, some of the older volcanic rocks of the Lake District and Wales were erupting and the Skiddaw slates were being deposited. 
 
Mosses and liverworts are found only on land and in freshwater, and are unique among complex land plants in lacking the lignified vascular tissue that all ferns, conifers and broad-leaved plants (collectively called "higher plants") have. For this reason they can't conduct large amounts or water or sugar solution up and down their stems, so can't grow very tall. Many can survive long periods of drought, and rehydrate and start to grow again when properly wetted.  Bryophytes reproduce and disperse through tiny spores rather than seeds,  and also vegetatively by fragmenting, and by special structures called gemmae.
 
Life cycle
Like ferns, bryophytes have two life stages, which differ in the number of chromosomes In their cells. In “higher” plants and most animals, the dominant or main life stage is diploid – with two copies of each chromosome, one from its female and one from its male parent. A haploid cell or organism has only a single set of chromosomes.  To reproduce sexually, diploid organisms first need to halve the chromosome count, producing haploid eggs and sperm. When these come together and fuse, the diploid chromosome count is restored and an embryo can form.
 
In mosses and liverworts by contrast, the dominant life stage is the haploid phase called the gametophyte, because it produces gametes - eggs and swimming sperm.  Fertilised eggs grow into the diploid or sporophyte stage which is small and remains attached to the parent female gametophyte.  It is confined to producing the next generation of haploid spores. When these germinate they grow into the next haploid gametophytes.  The structure containing the spores is called a sporangium (plural sporangia), often held on a slender upright ‘stalk’ called a seta, which allows the minute  spores to be released above the ground making for better dispersal.
 
This two-stage life cycle is sometimes call "Alternation of Generations" In some algae both life stages are equally prominent.  In the ferns it is the sporophyte, in the bryophytes the gametophyte, and the sporophyte is usually very small and inconspicuous.
 
 
 
 
 
 
 
Bryophytes also reproduce asexually, producing "gemmae"which are asexual cells or groups of cells, often produced in specialised little cups, that can detach and form a new plant. Think of these as the equivalent of a gardener taking some cuttings. More haphazardly, any bit of broken bryophyte falling onto the right sort of ground conditions can grow into a new plant – good job they are small or they could take over our gardens.
 
Gemmae developing in cup-like structures on the liverwort Marchantia polymorpha 
Moss or liverwort?
 
The two groups are quite easily distinguished.  If there is no clear differentiation into leaves and stems, and the plant body is deeply segmented or lobed, it is a thalloid liverwort. If it has a stem with leaves in ranks arranged laterally (sometimes with three ranks of leaves, the third smaller and under the stem), it's a leafy liverwort. There is more about liverworts on our page here.
Thalloid liverwort Conocephalum conicum Leafy liverwort Plagiochila porelloides
 
Mosses all have differentiated stems and leaves, and the leaves are never arranged strictly in ranks, and generally surround the stem, leaves are small, and can be rather like scales. They can form neat cushions, often with prominent sporophytes, or appear as straggly bunches. We show something of the variety of mosses on our page here.
Studying bryophytes
 
Even though bryophytes are common everywhere, indeed, appearing on all continents including Antarctica, they are often ignored – possibly owing to their small size, lack of familiar features like flowers,or the difficulty of identifying them when they are dried up and shrivelled in droughted conditions. But they are really beautiful if you take the time to look.
 
They grow everywhere and anywhere – on tree trunks and branches, in lawns and meadows, in woods, in water, on roofs, on gates and walls, on paving stones, in the little gaps between surfaces and on soils. There is an enormous diversity of shape, colour, and structure. Many have their own fungal associates; others are full of little invertebrates like springtails and mites. They are a home to a myriad animals. They protect your soil from drying out and happily contribute more carbon to your soils’ organic matter because they grow slowly. So get out your hand lens, magnifying glass or microscope, collect little samples, put into a thin film of water so they can rehydrate and then have a close look under a good table lamp.
 
 
References
 
1.  Li,F-W, et al (2020) Anthoceros genomes illuminate the origin of land plants and the unique biology of hornworts.  Nature Plants 6:259–272  Available here.
 
Finding out more
 
Books
Atherton, I.,Bosanquet, S. and Lawley, M.  (2010).  Mosses and liverworts of Britain and Ireland: a field guide. British Bryological Society
Field Studies Council  Garden mosses guide
Porley, R. and Hodgetts, N. 2005 Mosses and Liverworts Collins New Naturalist Library (97)
 
Websites
Bryophytes website (UK)
Bryophyte identification guidance 
British Bryological Society website   
Bryophytes of Britain and Ireland Facebook Group 
 
Page written by Penny Anderson, compiled by Steve Head
Field hornwort Anthoceros agrestis
 
There is just a chance you might find this in a damp area of your garden.
Typical mosses  Grimmia pulvinata              Brachythecium rutabulum 
 
Hornworts
Purely for completeness, we mention another bryophyte group, the hornworts (not to be confused with the pond plants of the same name). Hornworts form a small group, with only four species in Britain and Ireland, and of these, field hornwort Anthoceros agrestis is the most widely distributed.  They are not uncommon in damp stubble fields and woodland margins, and probably could occur in rural gardens.  Hornworts have uniquely algal-like features as well as other features more like vascular plants.1.  The gametophyte is the main life stage and rather like a thalloid liverwort, but the sporophytes (the horns) are large and green and potosynthetically self-sufficient.
 
 
       Garden Wildplants
             Garden Wildplants