Introduction to the genus Sphagnum, Some notes on identification, by Martin Godfrey

Introduction to the genus Sphagnum Some notes on identification

Sphagnum squarrosum

Martin Godfrey

Contents Introduction The genus Sphagnum – Part 1: A guide The genus Sphagnum – Part 2: Sphagnum palustre, S. papillosum and S. magellanicum The genus Sphagnum – Part 3: Sphagnum fallax and S. angustifolium The genus Sphagnum – Part 4: Small red Sphagna The genus Sphagnum - Part 5: Section Squarrosa The Genus Sphagnum – Part 6: Microscopy The Genus Sphagnum – Part 7: Sphagnum fimbratum and S. girgensohnii The Genus Sphagnum – Part 8: Section Subsecunda

SPHAGNUM – USEFUL READING Appendix 1: Referees

Introduction The Sphagnum mosses as a whole are wetland species, some forming large raised bogs whilst others form mats and hummocks, or even floating carpets, in a variety of wet habitats, including woodland, heath, flushes and mires. They are one of the few groups of bryophytes which can actually be dominant in some habitats and, even when they are not, can form a conspicuous and important part of the flora. Worldwide this importance is reflected in the sheer amount of carbon sequestered annually by the genus, somewhere in the region of 200 million tons – it is suggested by many authors that, in terms of biomass, they are the single most important plant genus in the world.

At a more local level they can be a very important indicator of the “health” of the environment. Like all bryophytes Sphagna get their water directly over their whole surface, making them sensitive to pollution; however they also have a cation exchange mechanism in their cells which modifies the environment and makes them particularly sensitive to diffuse pollutants which they pick up. Thus changes in the Sphagnum cover in an area can quite quickly reflect environmental change.

Given the importance of the genus, which is really easy to identify, why do we need to take care to identify the individual species? Indeed in many ecological reports which I have read just the presence of the genus is recorded. The fact is that, contrary to the belief of some, they don’t all share the same ecological niche and the subtle differences in requirements between species can give early warning of change. For example if the rather rare Sphagnum pulchrum vanishes from a site you can be sure that your bog is drying and becoming more eutrophic. Even within an individual section of the genus this can show up – S. papillosum and S. magellanicum both require rather oligotrophic conditions whereas the very similar looking S. palustre is happy under a eutrophic regime, so the reduction or disappearance of the first two to be replaced by the third is a clear sign that all is not well. Indeed to my mind the lovers of rather eutrophic conditions S. squarrosum and S. fimbratum are clear indicators of degraded wetlands.

This booklet is a reprint of a series of articles I have written for the Shropshire Botanical Society Newsletter over the past few years. Its purpose remains the same, to encourage the botanist who may have no great knowledge of bryophytes to include accurately identified sphagnum mosses in their species lists and reports, the better to understand the environment. And of course to have fun looking at this fascinating and attractive group of plants.

Martin Godfrey, November 2017

The genus Sphagnum – Part 1: A guide

Many botanists seem to be able to pass their whole lives without giving the bryophytes more than a superficial glance before passing them by as “too difficult”. They do, however, often form a significant part of a floristic assemblage and I would maintain that at least a working knowledge of the genus Sphagnum is essential if you are going to take a serious interest in plant ecology. The purpose of this article is to give a gentle introduction to the structure of the plants so that you can make a start on using keys; I hope to follow it up with a couple of articles focussing on individual species and species groups.

Most botanists can recognise sphagna to genus level without difficulty; they are a familiar component of wet habitats such as woods, mires and heaths and may even, on occasion, grow submerged. When well grown they typically form sometimes brightly coloured carpets or hummocks and, by moss standards, are really quite large. In common with many other large and brightly coloured plants, particularly when there are illustrated guides to hand, there is a temptation to identify by “jizz” and quickly move on to the next plant. However sphagna are not always found to be well grown and are morphologically somewhat plastic so are perhaps best treated like grasses and sedges as plants which need a bit more concentration. Although for convenience I will illustrate this article with a few microscopic images, for basic identification you will need nothing more than your hand lens. It is sometimes necessary to use a microscope to identify difficult specimens but, for the complete beginner, it might be better to submit such specimen to a referee.

To make a start you first need to look at the individual Sphagnum plant rather than the cushion. To do this extract one or two shoots from the cushion or turf and look at it closely – you will see that it consists of three main parts: A pom pom like structure on the top of the stem known as the capitulum. This is formed from short branches.

The stem itself.

Arranged along the stem bundles of branches known as fascicles.

Further examination with your lens will show that the stem and branches are covered in tiny leaves.

Note the colour of the plant and the distribution of colour between the leaves and stem. Presence of a colour is a very useful identification feature; the snag is that colour only tends to develop properly in good light so a plant which might otherwise be deep wine red can be green if growing in the shade.

That said if colour would usually be present it is often possible to find some scraps of it by careful examination with a lens.

To start your identification you will need to dissect the plant; with a bit of practice this is quite easy to do in the field with your fingers.

First remove the capitulum and put it on one side. If you examine the stem carefully you will see that the individual fascicles of branches all leave the stem at one point – carefully remove several fascicles and put these on one side also.

Having done your dissection first take a look at the capitulum and see if it has a big bud protruding from the middle – if there is one they are usually fairly obvious so if you are scrambling around trying to see one then there probably isn’t one there.

A particularly important identification feature is the structure of the individual fascicles. First note that these are composed of both spreading and pendent branches. What you need to determine is firstly if the spreading and pendent branches look different from one another and also the relative lengths – are they similar in length or is one set longer than the other. It is also useful to know if the spreading branches are curved.

You should then count the number of spreading and the number of pendent branches – you might need to use something like a grass stem to help you as pendent branches can stick together. While examining the branches make a note of the shape of the leaves.

Next take a look at the broken end of the stem through your lens and see if there is a wide cortex around the central dark patch – if there is one it will be quite obvious.

The final step in gathering your identification information is to look at the stem leaves. Once you have removed a number of fascicles you will leave a length of bare stem. Look at this bare stem carefully and you will see that it is covered in leaves – these are usually a totally different shape from the branch leaves – note the shape and orientation (pointing up the stem, hanging or spreading) of these leaves.

Stem leaves can, for example, be tongue shaped, elliptical or triangular and have blunt or pointed leaf tips. You will also get some idea of their relative size; some leaves look surprisingly large relative to the stem and some minute.

You now have enough information to enable you to use one of the keys in the publications mentioned below to make a start on identifying your Sphagnum. As with all new skills identification of sphagna takes time and practice so don’t despair if it doesn’t work first time.

The genus Sphagnum – Part 2: Sphagnum palustre, S. papillosum and S. magellanicum Introduction In the previous edition of the “Newsletter” I gave an overview of the structure of Sphagnum plants to help botanists who would like to identify these plants to species. In this edition I provide some identification notes to three of the larger species.

General All three of these species are in the section “Sphagnum” of the genus and are characterised by their large size and “chunky” appearance with broad, concave and “hooded” branch leaves and the broad stem cortex mentioned in the previous article. S. palustre has the broadest ecological amplitude of the three and may be found in wet woodland as well as bogs, mires and flushes. S. papillosum and S. magellanicum are both more typical of raised bogs and mires and are generally less shade tolerant than S. palustre.

S. magellanicum This species is unlikely to be confused with the other two as it grows in deep hummocks with the individual plants having a deep wine red colour making it very conspicuous – Fig. 1.

Fig. 1 S. magellanicum The only other species which grows in wine-red mounds on bogs is S. capillifolium which is much smaller, has fine pointed leaves and does not show the broad stem cortex.

S. palustre and S. papillosum Although when well grown these two species are reasonably easy to distinguish, they are frequently confused and so are dealt with here together.

S. palustre is usually more or less green in colour, although it may show some ochre in the middle of the capitulum, and grows in rather loose carpets or mounds – Fig. 2.

Fig. 2. S. palustre S. papillosum on the other hand is usually brownish/ochre in colour and grows in tightly packed mounds or carpets – Fig. 3.

Fig. 3. S. papillosum The ID problems can arise when the plants are growing sub-optimally when they can look very alike.

The solution here is to compare the structure of the branch fascicles. In S. palustre the spreading branches are long, tapering to a point, and the hanging branches can be quite wispy. In S. papillosum the spreading branches are short and blunt and the hanging branches proportionately shorter than in S. palustre – Fig. 4.

Fig. 4. S. palustre

S. papillosum

If all else fails it is possible to use a microscope to compare the structure of the branch leaf cell walls – those of S. papillosum are roughened (hence its specific name) whereas those of S. palustre are smooth – Fig. 5 and 6.

Fig. 5. S. papillosum cell walls

Fig. 6. S. palustre cell walls.

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The genus Sphagnum – Part 3: Sphagnum fallax and S. angustifolium Introduction In this third part of my overview of the genus Sphagnum I am going to provide some identification notes on two species which can be quite hard to distinguish in the field.

General Both of these species are in section Cuspidatum of the genus Sphagnum. This section is characterised by star-like capitula with developing branches in pairs and stem leaves which hang downwards, see Fig. 1. Both species are quite common and occur in a variety of nutrient-poor wet sites and, although they have somewhat different ecological requirements (see below), they may occasionally be found growing together. S. fallax is probably the commoner of the two but, given the similarity in overall appearance, S. angustifolium may well be under-recorded for S. fallax.

As we are going to look at the morphology of the branch fascicles and the shape of the stem leaves to distinguish these two species you are going to need to carry out the simple dissection of a single plant outlined in part 1 of the guide – remove the capitulum then carefully take off several branch fascicles and put them to one side.

Figure 1. Hanging branch leaves.

Sphagnum fallax This plant grows in lawns rather than hummocks and usually shows some yellowish-ochre colour when growing in well lighted situations, Fig. 2.

Fig. 2. S. fallax.

After completing your field dissection first take a look at the branch fascicle, you will see that the spreading and pendent branches are more or less the same length with the pendent branches usually being paler than the spreading, sometimes they are almost white, Fig. 3.

Fig. 3. S. fallax branch fascicle.

The leaves on the spreading branches are often clearly growing in straight lines and, when dry, are quite strongly curved. Next look at the stem leaf shape; note that this may need some effort as the leaf is small, one cell layer thick and the same colour as the underlying stem. You will see that the leaf is triangular – perhaps a bit longer than wide, about 0.75mm or so long and at least some of them will have a sharply pointed tip – as if the leaf had been pinched, Fig. 4.

Fig. 4. S. fallax leaf.

Sphagnum angustifolium Like S. fallax this species tends to grow in lawns rather than hummocks. But in my experience tends to be a bit smaller and less strongly coloured although this is by no means invariable, Fig. 5.

Fig. 5. S. angustifolium.

As with the previous species carry out your field dissection. This time when you look at the branch fascicle you will see that the pendent branches are conspicuously longer than the spreading branches Fig. 6 – note the conspicuous here, the difference is obvious, if it isn’t then you have S. fallax!

Fig. 6. S. angustifolium branch fascicle.

In this species the branch leaves are rather more untidy looking than in S. fallax although like that species the branch leaves curve when dry. Now look at the stem leaves – the same caveat applies regarding difficulty. In S. angustifolium the leaves are a little smaller than S. fallax, are more or less an equilateral triangle and have an obviously blunt leaf tip, Fig. 7.

Fig. 7. S. angustifolium leaf.

Ecology Generally speaking S. fallax grows in permanently wet, nutrient poor to intermediate habitats whilst S. angustifolium occurs more frequently in mineral-rich sites and is a bit more base demanding/tolerant.

Given these differences it is well worth taking a few minutes to correctly identify which species you have as a change in abundance of one over the other over time may indicate an ecological change in your site.

The genus Sphagnum – Part 4: Small red Sphagna Introduction In this fourth part of my overview of the genus Sphagnum I will provide notes on three small red species, as well as two subspecies – S. capillifolium (in the form of its two subspecies ssp capillifolium and ssp rubellum), S. subnitens and S. quinquefarium. These are by no means comprise all of the red Sphagna, indeed we have already looked at S. magellanicum in part two of the series, but they are the common species likely to be found when out botanising in Shropshire. Note that with all these species in shady conditions, such as partially under heather, the plants may be greener than red but close examination will usually reveal at least some pigment.

General All three of these species are in section Acutifolia of the genus Sphagnum. This section is characterised by a slender habit, the frequent presence of at least some red pigment, spreading and pendent branches being strongly differentiated (the pendent usually being long, slender and rather pale or even whitish in colour) and stem leaves which are upright, see Fig. 1.

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Fig. 1. Upright stem leaves.

The morphology of branch fascicles and the size and shape of the stem leaves is going to be important in distinguishing between these species so you will need to do the simple field dissection outlined in part 1 of the series to give you a small selection of intact fascicles and a bare stem on which you can see the upright stem leaves. Remember that the structure of fascicles can vary, even within a single specimen, so it is important to look at several to decide what is typical. In distinguishing the two subspecies of S. capillifolium you will be asked to measure the length of the stem leaves – this may seem impractical in the field but is, in fact, quite easy if you use one of the lenses which incorporate a mm measuring scale (well worth having for more general botany for measuring floral parts) – BSBI/Summerfield Books does a couple of models.

Sphagnum capillifolium This wine-red species forms compact hummocks or rather more spreading mats (see below) on damp moors and in bogs, Fig. 2. The stem leaves are ligulate, with more or less parallel sides, tapering at the end to give either a pointed or a rounded tip (see below). In this species the branch fascicles usually have four components, two spreading and two pendent. It is divided into two subspecies (in many Continental accounts these are given specific status; on the other hand there are some bryologists who

are sceptical of their existence at all as separate taxa) and it is well worth looking at these in detail and recording them as we don’t have a clear understanding of their distribution.

Fig. 2. S. capillifolium Subspecies capillifolium This subspecies forms tight, dense, mounds which feel firm to the touch and the capitula are distinctly pom-pom shaped, Fig. 3. The stem leaves have pointed (maybe even somewhat pinched) tips and are typically greater than 1.2 mm long.

Subspecies rubellum This subspecies forms rather loose mats and has a flatter, rather untidy looking, capitulum, Fig. 4. The stem leaves have a rounded tip and are typically less than 1.2 mm long. It may be found in somewhat dryer habitats than ssp. capillifolium.

In practice I find that the stem leaf length is a pretty reliable ID feature, the mound vs. mat growth form quite reliable and the capitulum shape less so. It is best to split the subspecies on as many features as possible.

Fig. 3. ssp. capillifolium

Fig. 4. ssp. rubellum (Both photos – Des Callaghan)

Sphagnum subnitens In our part of Britain this species frequents a number of wet habitats including flushes, heath and woodland edge and is less likely to be found in bogs. It grows in small soft mounds and cushions. The colour is more usually a salmon pink rather than wine red, in practice once seen it is quite distinctive.

The capitula often have rather greenish centres with the red colour confined to the edges which make this species stand out in the field (but beware less typical examples of the following species), Fig. 5.

The plant derives its specific name from the shiny character of the dry plants.

Fig. 5. S. subnitens.

The stem leaves are triangular and frequently have acute tips with inrolled margins. The branch fascicles usually have three members, two spreading and one pendent, Fig. 6.

Fig. 6. S. subnitens fascicle.

Sphagnum quinquefarium I have included this species because although it is usually more or less green throughout it can occasionally be quite red with a capitulum which may mimic that of S. subnitens to a casual glance. It also grows in similar habitats to the latter species although always on well drained ground and is absent from bogs and flushes – I find it quite frequently in wet woods. In growth form it produces often quite large, soft, hummocks and carpets. Fig. 7.

Fig. 7. S. quinquefarium.

The stem leaves are distinctly triangular but what makes it really stand out is its branch fascicle. This has five components - three spreading (the other members of sect Acutifolia have two) and two pendent, Fig. 8.

Fig. 8. S. quinquefarium fascicle.

The genus Sphagnum - Part 5: Section Squarrosa Introduction In this fifth part of the “Guide” I am going to look at section Squarrosa. This section only has two species, S. squarrosum and S. teres. The former is common and usually very easy to identify, the latter rather less common, being restricted nationally to more northern and western parts, and can also be rather more tricky to identify. Both species show the “big bud” feature in the capitulum (see Part 1 of the guide – News spring 2012) and either may have squarrose branch leaves – that is, leaves in which the tip is bent sharply back which, en-masse, gives the plant a rather prickly appearance. The branch leaves in both species have rather broad bases with long, narrow, leaf tips. The stem leaves are quite large and are broadly tongue shaped.

Sphagnum squarrosum This is quite a chunky plant, usually a light bright green in colour which invariably has squarrose branch leaves so that the whole mass of plants looks rather prickly, Fig. 1.

Fig. 1. S. squarrosum habitat picture.

The capitulum usually has a “big bud”, Fig. 2., although you may have to look rather hard for it.

Big bud in middle of capitulum

Fig. 2. Capitulum with bud Somewhat unusually for a Sphagnum it grows in nutrient enriched wet ground, often in woods or rather untidy grass and rush habitats. It is quite common and is usually found in carpets rather than hummocks, and these can be quite extensive.

There is really no other moss quite like S. squarrosum so it is usually very easy to identify. The only possible confusion species are some populations of S. palustre growing in shade. These can have rather squarrose branch leaves but these leaves have the broad hooded appearance and the stem the wide, easily visible, cortex of the plants of section Palustre (see part 2 of the guide, autumn 2012).

Sphagnum teres When growing well, the ginger colour of this medium sized species makes it quite conspicuous amongst the wet grass where it grows, Fig. 3.

Fig. 3. S. teres

It, too, usually has a conspicuous bud in the capitulum, Fig. 4.

Big bud in middle of capitulum

Fig. 4. S. teres capitulum with bud.

Despite its section it rarely has squarrose leaves, although these may develop in shade forms. Instead confirm the identification by looking for the usually dark stem and the 2-3 spreading branches in each branch fascicle. At times it can be rather anonymous and difficult to identify.

I usually associate this species with rather base-rich flushes where it grows either in small loose cushions or as a narrow band beside running water.

Problem plants Even though they don’t look much alike these species are placed in the same section based on very similar microscopic characters and it is to the microscope that you will need to turn if you find something you cannot place.

Distribution in Shropshire S. squarrosum is really quite common in the county and is found throughout, Fig. 5, although there are plenty of gaps for your new records!

S. teres on the other hand has a far more restricted distribution, Fig. 6. This may be a reflection of the lack of suitable habitat, on the other hand given that it isn’t a terribly obvious species I wonder if it might be under-recorded. An interesting challenge would be for you to get away from the Long Mynd area and go to flushes that you may know and see what you can find.

Sphagnum teres (Rigid Bog-moss) 5

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SJ 9

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SO 1

Fig. 5. Sphagnum squarrosum

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Fig. 6. Sphagnum teres

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The Genus Sphagnum – Part 6: Microscopy Introduction As an adjunct to this series of articles on the identification of Sphagnum I have been asked by a number of people if I could give some tips on microscopy, the better to be able to use the more advanced keys which are available. As I mentioned in my first article on the group, back in 2012, it is possible to identify most species with a lens in the field but this is conditional on the plants being well grown and typical. Plants in this genus can be morphologically very plastic making them, at times, difficult to identify and this is where the microscope comes in. There are many more identification features available at a microscopic level and these tend not to be variable meaning that you can usually get a reliable identification if you can use a microscope.

The purpose of this article is to describe and illustrate some of the more important microscopic features to help you identify your Sphagnum. For those of you unfamiliar with the microscope and the techniques I mention there will be a hands-on microscopy workshop at Preston Montford next autumn targetted specifically on Sphagnum – keep an eye on the programme for details.

Things to look for We will look at features in three parts of the plant – the stem, the stem leaves and the branch leaves.

The stem Here what we are interested in are the number of layers of cells in the stem cortex and, occasionally, pores in the outer cells of the cortex. (The cortex is the outer layer, or layers, of cells of the stem).

A thick stem cortex, visible with a lens, is a feature of section Sphagnum however the possession of one or more layers of cortex cells is also a diagnostic character for a number of species in the genus and to see these you will need a microscope. To see the stem cortex strip the capitulum and branches from your plant and cut thin sections of the stem with a fresh razor blade. Mount the resulting sections in a drop of water and examine under the medium power (x100) of the microscope. (Fig. 1). To see if there are any pores in the stem cortex cells and count and measure them if appropriate, strip a little of the cortex from the stem (previously stripped of capitulum and branches) and mount in a drop of water.

You may need to use a higher power (x400) to see the pores properly. (Fig. 2).

Cortex 1 cell layer

Cortex 2-3 cell layers

Cortex 4-5 cell layers

Fig. 1. Stem cortex thickness.

Pores

Fig. 2. Stem cortex pores Stem leaves Apart from the overall shape, which you can see with a lens, what we are interested in here are the presence, size and distribution of pores in the clear cells (hyalocysts) of the leaf , the presence and distribution of fibrils in the same cells and the presence and extent of thickened cells in the basal part of the leaf. To see these you will need to strip some stem leaves off the pre-prepared stem and mount them in a drop of water for examination – you will probably need to use all of the powers of your microscope in turn to see all of the features. (Fig. 3, 4 and 5).

Fibrils

Pores

Fig. 3. Pores and fibrils Fibrils in about 50% of leaf tip

Fig. 4. Extent of fibrils in leaf.

Thickened cells in leaf base

Fig. 5. Thickened cells Branch leaves In the branch leaves what we are interested in are the presence and distribution of pores in the clear cells on both the concave and convex surface of the leaf. Occasionally we also need to look at whether the green cell (chlorocyst) of the leaf is more exposed on the convex or concave side of the leaf. To look for pores strip some leaves from branches and mount in a drop of water - some with their convex surface upwards and some with their concave surface upwards – and examine using the medium and high powers of your microscope. (Fig. 6).

Pores (all around the cell margin)

Fig. 6. Branch leaf pores

Pores

To look at the exposure of the chlorocysts you will need to cut sections of branch leaves using a fresh razor blade and mount them in water to examine under the medium and possibly the high power of your microscope. For clarity I have illustrated the options with a drawing – Fig. 7 below.

Staining Occasionally it is difficult to see the features you are looking for under the microscope, especially when you are examining leaves. If you have trouble you can stain the specimen with a solution of gentian violet in alcohol or water. Put the specimen into a drop of the stain and leave for a couple of minutes.

Remove as much of the stain as you can with a bit of tissue and add a drop of water to the specimen before examining.

The Genus Sphagnum – Part 7: Sphagnum fimbratum and S. girgensohnii Introduction Over the past year or so I have had a number of records and specimens sent to me as Sphagnum girgensohnii which, on examination, have proved to be S. fimbratum. This short article will, I hope, clarify field ID features to enable you to identify plants with a lens.

What to look for Sphagnum fimbratum is common and abundant and is one of those few Sphagnum species which most people identify by a “jizz” feature. The stem leaves of this species have broad rather tatty (fringed or fimbrate) tips so when you remove the capitulum and look at the broken end of the stem with a lens you can see these leaves forming a conspicuous ruff around the stem – a characteristic which is exhibited by no other species. That said, although they are a totally different shape, the stem leaves of the rather scarcer S. girgensohnii also have fimbrate tips and I suspect that this, combined with a bit of optimism, is leading to the mistaken IDs. So how are we going to tell them apart? Both species look rather similar, being smallish and slender and always green – Fig. 1. They also have rather similar ecological requirements, being minerotrophic and shade tolerant, so you tend to find them growing in loose hummocks or mats in mineral rich conditions – often in wet woods. Both have a “big bud” in the centre of the capitulum, Fig. 2, but this is usually more conspicuous in S. fimbratum.

Bud Fig. 1.

Fig. 2.

There are two good features which will enable you to tell them apart. First look at the fascicle structure.

In S. fimbratum the fascicles are well spaced down the stem and usually consist of 3-5 branches, 2-3 of which are divergent and the others pendant. In S. girgensohnii on the other hand the fascicles are usually more crowded and consist of 3 branches, 2 of which are divergent and one pendant. The other feature is the leaf shape which is totally different in the two species. You should be able to see this quite clearly with a lens although for convenience I illustrate this article with photomicrographs.

In S. fimbratum the tip of the leaf is much wider than the base giving a very broad band of fringing which en-mass shows as the ruff at the top of the stem, Fig. 3.

Fig. 3. Sphagnum fimbratum stem leaf In S. girgensohnii on the other hand the stem leaf tip is narrower than the base so, notwithstanding the fact that it is fimbrate, you do not get the ruff effect seen in the previous species, Fig. 4.

Fig. 4. Sphagnum girgensohnii stem leaf.

Checking your ID As always if you find a confusing or difficult plant get a referee to have a look at it – Sphagnum girgensohnii is rare in the county and has not been seen for some time so in any event you would need to support a record with a specimen. For guidance on referees see Appendix 1.

The Genus Sphagnum – a guide part 8: Section Subsecunda Introduction This section is the one with rather untidily spreading/hanging stem leaves and frequently rather swollen, curved branches. When growing in good light the plants often have some yellow or coppery colour. In practice the section can be quite a tricky one to recognise and, with the odd exception, is the one in which I most often resort to the microscope for identification. Have a look at article 6 in this series for microscopy technique details, which you may need later.

There are five species from this section growing in Britain and all of them have been recorded for Shropshire. S. denticulatum and S. inundatum are quite widespread and common, S. contortum is rather scarce as is S. subsecundum (although this may be underrecorded as it is similar to S. inundatum) and S. platyphyllum is rare with just a few records.

It is probably most convenient to divide the section in two – S. denticulatum and S. platyphyllum which are relatively straightforward to identify and the other three, S. inundatum, S. contortum and S. subsecundum which can look very similar in the field.

S. denticulatum and S. platyphyllum When growing well S. denticulatum is a large conspicuous plant with swollen, curved branches, Fig. 1.

However it has quite a wide ecological amplitude and with this can be morphologically rather plastic – in shaded conditions it can look rather like S. inundatum whilst when growing submerged, Fig. 2, its bulky form can be rather suggestive of S. palustre.

Fig. 1. S. denticulatum

Fig. 2. Submerged S. denticulatum

A useful field feature to distinguish between S. denticulatum and S. inundatum is the structure of the fascicle – in S. denticulatum the spreading and pendent branches are not very different and there are 23 spreading and 1-2 pendent. In S. inundatum the spreading and pendent branches are clearly different from each other and there are 2-3 divergent and 2-4 pendent branches in the fascicle. If you get a really problematic plant then you will need to resort to the microscope. Here you will find that the stem leaves are almost completely fibrillose in S. denticulatum whilst in S. inundatum they are only 20% - 40% fibrillose.

S. platyphyllum, Fig. 3, is usually easy to identify in the field – although small it has rather short thick branches with only 1-3 branches per fascicle and rather large elliptical stem leaves. In all the other species in sect. Subsecunda the stem leaves are more or less triangular.

Fig. 3. S. platyphyllum S. inundatum, S. contortum and S. subsecundum All three of these species are rather small, slender, plants – indeed S. subsecundum can be a bit like S. capillifolium (albeit never red) – with branch fascicles of 2-3 spreading and 2-4 pendent branches. In the field they all look rather alike, Fig. 4, note the rather curved branches as a good indicator for this section of the genus.

Fig. 4. S. inundatum When well grown both S. inundatum and S. subsecundum have dark (even blackish) stems but the former is much the larger and has longer stem leaves, typically over 1mm and up to around 1.5mm, whereas S. subsecundum is a slender plant with stem leaves mostly under 1mm, ranging from around 0.5mm – 1mm. Apart from being slender and pale I find S. contortum a challenge in the field and I will usually take it home to check under the microscope. When not terribly well grown the first two species will often come home too for microscopic checking when the ID of all three can be quite straightforward.

A stem section will show that S. contortum has a cortex 2-3 cell layers thick, whilst the other two have a cortex one cell layer thick, Fig. 5. To separate S. inundatum from S. subsecundum you will need to examine the fibrils in the stem leaf cells, Fig. 6 – the former is fibrillose for 20% - 40% of its length while the latter is fibrillose for 0 – 25% of its length.

Fig. 5. Stem cortex thickness.

Fibrils in about 50% of stem leaf

Fig. 6. Extent of fibrils in stem leaf.

SPHAGNUM – USEFUL READING Here is a list of books which you may find useful; the general books all have sections on Sphagnum and “Smith” is the current standard work on British mosses.

Sphagnum Daniels RE and Eddy A (1985). Handbook of European Sphagna. Institute of Terrestrial Ecology. Out of print but worth searching for as it is a very comprehensive manual of the genus. Available as a free download from http://nora.nerc.ac.uk/8498/ Hill MO, revised Hodgetts NG and Payne AG. (1992). Sphagnum: a Field Guide JNCC. Nomenclature out of date (but simple to fix) but still probably the best field ID guide.

Holzer, A (2010). Die Torfmoose Sudwestdeutschlands und de Nachbargebiet. Weissendorn Verlag, Jena. In German with keys duplicated in English. A superb handbook with outstanding illustrations. If you can manage a bit of German the sections on ecology are first class.

Laine J et al (2011). The intricate beauty of Sphagnum mosses. University of Helsinki. A new publication with truly outstanding illustrations, both of the whole plants and microscopic features.

General Atherton I, Bosanquet S and Lawley M (eds) (2010). Mosses and Liverworts of Britain and Ireland, a Field Guide. A new, fully illustrated, guide which is likely to prove a standard work for all beginners and students.

Porley, R. & Hodgetts, N. (2005). Mosses and Liverworts. Collins. A quite outstanding, addition to the “New Naturalist” series. If you read nothing else read this.

Watson, E.V. (1981). British Mosses and Liverworts. 3rd ed. Cambridge University Press. This is the standard beginners and students flora. Despite its age it is an excellent introduction to the group.

Smith, A.J.E. (2004). The Moss Flora of Britain and Ireland. 2nd ed. Cambridge University Press.

This is the current standard moss flora.

Dixon, H.N. & Jameson, H.G. (1904). The Students Handbook of British Mosses. Sumfield, Eastborne.

2nd ed. Although old the various editions of this handbook are still a mine of useful information.

Blockeel, TL, Bosanquet SDS, Hill MO & Preston CD (2014). Atlas of British and Irish Bryophytes. An entirely new Atlas with much excellent interpretative material.

Hill MO, Blackstock TH, Long DG and Rothero GP(2008). A Check-List and Census Catalogue of British and Irish Bryophytes. Updated 2008. British Bryological Society. The current checklist for the group.

British Bryological Society Website: www.britishbryologicalsociety.org.uk – lots of useful information, pictures and links.

Appendix 1: Referees There will be occasions when you either cannot identify a specimen or have made an attempt but lack the confidence to be sure of your ID. This is the time when you need to consult a referee to help you.

Your first port of call would normally be your BBS county recorder, details under “Recording” at www.britishbryologicalsociety.org.uk . Most county recorders are happy to check your IDs or identify intractable specimens – the normal procedure would be to contact them first and then send specimens for checking. This isn’t meant to be a free general ID service so recorders will expect you to have made some attempt to identify your specimen, typically you will say what you have done in your email, and not flood them with a stack of specimens. In return you will get an ID, either a confirmation of yours or new, and hopefully an explanation of what the key ID features are, especially if you were wrong.

When contacting your VCR check how they would prefer the specimen, dry or fresh, and if fresh make sure that you seal it in a little ziplock bag before sending it. I have received many damp envelopes with a soggy hole where the specimen has fallen out.

If you live in a county with no VCR or they are not happy with the genus Sphagnum (there are a few) then you will need to consult the national referee – details under “Resources” on the BBS web site.

VCRs who cannot identify specimens tend to use national referees and there are occasions when even they cannot identify something so the specimen goes to the international authority on the genus. The rules for genus referees are well explained on the referees page.

I would encourage you to use VCRs to check your material as an excellent way of improving your skills. It has certainly been my experience that checking IDs for recorders builds up their confidence and skill very quickly – they are frequently right anyway and just need the confirmation and when they are wrong knowing why will help future work.