Fred Rumsey of the Natural History Museum, who gave this talk, is one of the small band of between 20 and 30 enthusiastic recorders of bryophytes in Britain. The name ‘bryophyte’ covers an agglomeration of three, not necessarily closely related groups with superficial similarities. These are the mosses, the liverworts and the hornworts. What they do have in common is a lack of vascular tissue, so being without ‘plumbing’ they are dependent on a degree of immersion in water, soaked up from below or collected from above. They also need water in order to reproduce, as many have mobile ‘sperm’ which swim from male to female plant, or part of plant. But some can also disperse vegetatively, through pieces breaking off the plant.
The bryophytes are an ancient group, but not a dead-end, as some show signs of active evolution as they find new niches. They are first colonisers, stabilising the ground for other plants to follow them, and also good indicators of soil and air condition. For its size, the UK has a surprisingly large proportion of the known species, including 60% of the European species. This is thanks to our very diverse range of substrates and underlying geology.
Of the three groups, the hornworts are probably the least known, and contain by far the fewest species. They are odd-looking beasts, rather like ‘candles in holders’. The number of sites for one old established species, Anthoceras agrestis, has declined drastically with the more frequent turning of agricultural soil. Liverworts are more frequently encountered, as they are found almost everywhere, including sand dunes, cracks in paving, and even floating (as on the Basingstoke Canal). They are distinguished by the lack of midribs in their triple-ranked leaves, which have tiny white breathing holes. They have a basal thallus on which sit cups containing egg-like spore sacs, much like those of the bird’s nest fungus. Some are very colourful, in shades of purple. As our knowledge of liverworts grows, so does the number of species, as old species are split up; but at the same time many species are lost to pollution because, like lichens, they are very sensitive to sulphur dioxide.
By far the largest and best-known group of bryophytes are the mosses. These are divided into ‘upright’ and ‘spreading’ species. All have distinct midribs in their leaves, and all produce stalks on which seed capsules then develop. They have the ability to dry out in times of drought, but revive with the return of rain. Some species are almost everlasting if not severely disturbed.
Among the most familiar mosses are the Polytrichales, the tallest ones, and the sphagna which create most peat. One species, Sphagnum austinii, is responsible for most of the old peat in the country, but is now very rare in the live state. There are 30 species of Sphagnum in Britain, a large percentage of the European list. Among the less familiar are the Splachnaceae, which colonise dung or dead animals. They produce colourful capsules that give out heat and a carrion smell, attracting insects to which the spores stick and are carried to new sites. Tetraplodon settles on dead sheep, and eventually preserves the shape of the corpse long after it has disappeared! Another species colonises the pellets of birds of prey.
Another, now rare species is equipped with mini-grapnels by which it latches onto birds. One very rare species is found only on lead spoil on acid ground; the spoil heaps from Roman workings at Charterhouse, in the Mendips, is its stronghold. Another favours zinc, but all the plants in Europe are male! There are females in the USA, but the two haven’t been brought together yet. Similarly, on the Three Peaks in the Yorkshire Dales there is a moss with the sexes on separate walls and seemingly unable to bridge the gap!
Thatch moss, on ageing straw, is now becoming rare as crumbling thatched roofs become a thing of the past. Fred suggests that it may be spread by birds. Knot-hole moss is found only in wound cracks on old beech trees on acid soil. Some former rarities are now doing well, such as one on elder trees. The successful ones are usually those with good dispersal systems, able to react to improved conditions. But there is a danger that increased aerial nitrogen could throw these gains into reverse.
One alien moss, Campylopus introflexus, has been so successful that it might claim the title of ‘most invasive plant’. Since 1941 it has expanded its range to cover all of the UK and Ireland. On heathland and other acid areas in can carpet the ground. It can survive dry for five years, and its effect on other wildlife has yet to be measured. Nonnative liverworts likewise have escaped into the wild, mostly brought here by the trade in exotic plants. Lophocolea semeteres arrived here from Australasia in 1985 on tree ferns, and is now widespread. Lophocolea brookwoodeana is our local speciality alien, only discovered two years ago in Brookwood Cemetery. It is similar to L. semeteres, but no exact match has been found in the world. Will it prove to be a pest?
In the matter of conservation, 37 species are protected by the Wildlife & Countryside Act. There are 67 BAP species, and 111 species proposed for protection. Common names have been given to a lot of species, as has happened with fungi. Some may be dreadful, but ‘goblin’s gold’ seems very fitting for one that glows at the entrance to rabbit burrows!
For those interested in increasing their knowledge of bryophytes, Fred recommends the excellent book, ‘Mosses & Liverworts of Britain & Ireland’, published by the British Bryological Society, lavishly illustrated with photographs. The BBS also holds outdoor meetings and workshops which we are encouraged to attend, but our best bet is to start by learning a few of our most familiar everyday species, and take it from there, as far as we wish. Thanks to Fred for bringing to vivid life this neglected group of plants.
Dick Alder