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Moss characters

Details of the leaves

Character menu

The character categories and their possible forms are:

Plant growth habit

Shoot growth form / colour

Arrangement of the leaves

Details of the leaves

Hairpoint:
- Present
- Absent
Leaves recurved, hooked, squarrose Note:
Apices bent abruptly to the side or downwards
Costa:
Teeth:
Leaf margins:
- Recurved
- Not recurved
Leaf surface:

Reproductive structures

Distinctive gemmae present:
Colour of seta:
- Yellow
- Orange
- Red
- Brown
Form of the capsule: Note:
Distinctive capsules only.

Western bryophytes

The wonderfully-named glen "My Lord's Throat", east of Alford, Aberdeenshire, has a surprisingly western bryophyte flora for a location on the east of Scotland.

Granite boulders are strewn over the steep slopes in this birch woodland, providing a niche for species favouring acid rocks. The photo shows a rich-green mound of Polytrichum accompanied by paler cushions of Bryum.

When a leaf is not a leaf

The green moss plant is not a diminutive, reduced version of a flowering plant

Bryophyte "organs and tissues" may resemble those of vascular plants, but they must have evolved separately and are not homologous morphological structures. To see why this is so, you have to remember that the leafy moss plant, the gametophyte, comprises haploid cells. Cells of this ploidy in flowering plants are found in the pollen grains and the ovules, while the leafy shoots are part of the diploid sporophyte plant body. The sporophyte on mosses comprises the semi-parasitic seta and moss capsule.

And so although we use terms such as shoot and leaf to describe parts of mosses that play similar roles to the same-named parts in vascular plants, they arise in a different generation in the life cycle. If a pollen grain or ovule developed photosynthetic shoots and leaves, we'd have something more akin to the moss gametophyte.

The overall similarity in plant structure between moss gametophytes and vascular plant sporophytes must be the result of convergent evolution.

To reflect these different origins, technical terms for the shoot-like and leaf-like parts of mosses have been defined, although these are rarely used by bryologists. However, this distinct nature of moss parts is worth bearing in mind and may go some way to explaining the ways in which moss "shoots" and "leaves" can demonstrate innovations in form and structure that are not found in vascular plants.

Corrie of Balglass

Cloch Burn drops over the cliffs at the Corrie of Balglass near Fintry, Stirlingshire, creating a variety of niches inhabited by a range of mosses and liverworts.

Bryophyte books

Here's a list of the bryological texts on my bookshelf:

Hairpoint present

Syntrichia ruralis ssp. ruraliformis has very conspicuous hairpoints, as do many of the Syntrichiums. Note the rough edges on the hairpoint margins, almost like teeth.

Hairpoints vary in their length relative to the leaf, some just projecting slightly from the leaf apex while others can be longer than the leaf "blade" iteself.

As hairpoints are generally unpigmented, they perhaps help reduce water loss by the leaves through reducing air flow over the leaf surfaces, while not interfering with light penetration to the photosynthetic cells of the moss.

No hairpoint

Atrichum undulatum
Amblystegium serpens
Andreaea
Aulacomnium androgynum
Aulacomnium palustre
Barbula sardoa
Barbula unguiculata
Brachythecium populeum
Brachythecium rutabulum
Bryum alpinum
Bryum argenteum
Bryum pallens
Bryum pseudotriquetrum
Calliergonella cuspidata
Ceratodon purpureus
Cratoneuron filicinum
Ctenidium molluscum
Dicranoweisia cirrata
Eurhynchium striatum
Calliergon giganteum
Climacium dendroides
Fissidens bryoides
Funaria hygrometrica
Gymnostomum aeruginosum
Gyroweisia tenuis
Homalothecium sericeum
Hylocomium splendens
Hypnum cupressiforme
Hypnum jutlandicum
Kindbergia praelonga
Leucodon sciuroides
Mnium hornum
Orthotrichum cupulatum
Orthotrichum rivulare
Orthotrichum stramineum
Palustriella commutata

Homalothecium sericeum (Brachytheciaceae)

Hairpoint absent

It's not very easy to show a photograph of a character that does not exist! The example of a moss with no hairpoint I've chosen here, Homalothecium sericeum, has interesting longitudinal folds on the leaves.

Philonotis fontana
Plagiomnium ellipticum*
Plagiothecium undulatum
Pleurozium schreberi
Pohlia melanodon
Pohlia wahlenbergia
Pseudocrossidium revolutum
Pseudoscleropodium purum
Pterygonium gracile
Racomitrium fasciculare
Rhynchostegium confertum
Rhytidiadelphus loreus
Rhytidiadelphus triquetris
Rhizomnium punctatum
Schistidium rivulare
Thamnobryum alopecurum
Tortella tortuosa
Trichostomum brachydontium
Ulota bruchii
Ulota phyllantha
Warnstorfia fluitans

Hairpoints are important, and much discussed, diagnostic characters, particularly regarding their length relative to the length of the leaf. I was therefore surprised at the length of the list here, comprising numerous common UK moss species, all with no hairpoint.

I've not yet attempted to see if there's any correlation between presence / absence of hairpoints and the nature of the niches inhabited by each group of mosses.

Recurved, hooked, squarrose

Ctenidium molluscum
Palustriella commutata
Rhytidiadelphus squarrosus

Palustriella commutata (Amblystegiaceae)

Recurved leaves

The illustrated moss is Palustriella commutata whose leaves are described as circinate-secund, i.e. curved and arising from one side of each shoot.

I've combined a range of features in this single character, as there appears to be few species that show these leaf forms. The essential feature highlighted is that the leaves are bent along their long axis in one way or another.

It seems reasonable to assume that any degree of folding of moss leaves will tend to help retain moist air, but at the expense of not presenting as much of the leaf surface perpendicular to the rays of the sun, compared to what properly-oriented flat leaves can achieve.

Excurrent nerve

Bryum capillare
Fissidens bryoides
Funaria hygrometrica
Plagiomnium ellipticum*
Syntrichia laevipila
Syntrichia ruralis
Tortula muralis

Syntrichia laevipila (Pottiaceae)

Excurrent costa

Species in the genus Syntrichia make a good subject for comparing variations in costa length relative to the leaf. In S. laevipila the costa clearly projects beyond the rounded leaf tip.

The example shown here of a moss with an excurrent costa, illustrates the character very clearly. It can be seen that the costa is devoid of pigmentation after it leaves the leaf "blade", becoming a hyaline hairpoint.

The costa is associated with structural rigidity and perhaps some degree of water transport, but after it transitions into a hairpoint, it's role may be primarily to reduce water loss.

Percurrent nerve

Atrichum undulatum
Aulacomnium androgynum
Aulacomnium palustre
Barbula sardoa
Barbula unguiculata
Brachythecium rutabulum
Bryum alpinum
Bryum pallens
Bryum pseudotriquetrum
Ceratodon purpureus
Climacium dendroides
Dichodontium palustre
Dicranoweisia cirrata
Fissidens dubius
Philonotis fontana
Pogonatum aloides
Polytrichum commune
Polytrichum piliferum
Orthotrichum rivulare
Orthotrichum stramineum
Palustriella commutata
Plagiomnium ellipticum*
Pseudocrossidium revolutum

Rhizomnium punctatum (Mniaceae)

Percurrent costa

The large broad leaves of the moss Rhizomnium punctatum have a conspicuous costa, making it easy to see how far it progresses along the length of the leaf.

Racomitrium fasciculare
Rhizomnium punctatum
Schistidium rivulare
Tetraplodon mnioides
Trichostomum brachydontium
Ulota bruchii
Ulota phyllantha

Of the mosses with a costa but no hairpoint, the majority appear to possess a costa which reaches the tip of the leaf, rather than stops short of it.

This could, perhaps, be considered the optimal arrangement of the costa from an "engineering" point of view, maximising both the strength and water transport functions of the structure.

Nerve almost reaches leaftip

Aulacomnium androgynum
Brachythecium populeum
Gyroweisia tenuis
Kindbergia praelonga
Mnium hornum
Pohlia melanodon
Pohlia wahlenbergia
Thuidium tamariscinum

Mnium hornum (Mniaceae)

Costa nearly reaches tip

Mnium hornum is a very common woodland moss forming loose dull-green carpets. A closer look at a single shoot shows not only anatomical details, but also reveals great beauty.

In mosses with very small leaves, determining whether the costa reaches the leaftip or not can be difficult. However, Mnium hornum, with it's relatively large spreading leaves, shows the costa detail very clearly.

Presumably there's little difference in functionality between costas that reach, and those that almost reach, the leaf tip.

Nerve ½ to ¾ length of leaf

Brachythecium albicans
Bryum argenteum
Eurhynchium striatum
Pseudoscleropodium purum
Rhynchostegium confertum

Brachythecium albicans (Brachytheciaceae)

Costa ½ to ¾ length of leaf

The leaves of Brachythecium albicans very much overlap one another and are appressed to the shoot, making determination of the costa length difficult. However, with good lighting you can see that the costa runs about ¾ up the length of the leaf in this species.

There appears to be few mosses with a costa in this proportion to the leaf, making it a useful diagnostic character.

Nerve about ¼ length of leaf

Pterygonium gracile*

Pterygonium gracile (Leucodontaceae)

Costa ¼ length of leaf

Even in this close view of some shoots of Pterygonium gracile the costa cannot be discerned due to the way the leaves overlap one another. Removing a leaf for closer inspection should reveal the short costa.

There appears to be few mosses with a costa in this proportion to the leaf, making it a useful diagnostic character - if you can see it!

Double nerve present

Hylocomium splendens*
Hypnum cupressiforme*
Hypnum jutlandicum
Plagiothecium undulatum
Pleurozium schreberi*
Pterygonium gracile*
Rhytidiadelphus loreus
Rhytidiadelphus triquetris

Plagiothecium undulatum (Plagiotheciaceae)

Double nerve present

Even this close view of well-hydrated leaves of Plagiothecium undulatum fails to reveal any double nerves.

Many of the species whose leaves can have a double nerve, include individuals where nerves are absent. Furthermore, the two nerves may be of different length, or one may not be developed at all in some specimens.

Costa absent (or very inconspicuous)

Calliergonella cuspidata
Ctenidium molluscum
Hedwigia stellata
Leucodon sciuroides
Hylocomium splendens*
Hypnum cupressiforme*
Pleurozium schreberi*

Calliergonella cuspidata (Amblystegiaceae)

Costa absent or apparently so

It's pretty hard to illustrate a negative, and many mosses do have very small nerves, but in this close view of a shoot of Calliergonella cuspidata, no nerve is visible. The character would help where you are considering one of these species but note the presence of a nerve in the specimen to be determined.

Most of the common mosses, at least, have a nerve or costa, and so the absence of this character is a useful diagnostic.

It would be an interesting exercise to see if there's any correlation between moss species lacking a costa, and the environment they occupy. Avalability of moisture comes to mind, but C. cuspidata is found in wet environments while H. stellata is often found on exposed rock surfaces in elevated locations.

Teeth on leaf margins

Atrichum undulatum
Aulacomnium palustre Note:
Teeth only present towards the tip of the leaves.
Bartramia pomiformis Note:
Teeth only present towards the tip of the leaves.
Brachythecium plumosum Note:
Denticulate.
Brachythecium rutabulum Note:
Denticulate.
Breutelia chrysocoma
Bryum rubens Note:
Commonly faintly toothed towards leaf tip.
Climacium dendroides Note:
Branch leaves coarsely toothed towards leaf tip; stem leaves smooth.
Cratoneuron filicinum
Ctenidium molluscum
Dicranella rufescens Note:
Denticulate at least above.
Dicranum fuscescens Note:
Toothed towards leaf tip.
Dicranum majus Note:
Sharply toothed towards leaf tip.
Dicranum scoparium Note:
Variously toothed towards leaf tip.
Eurhynchium striatum
Fissidens adianthoides Note:
Toothed towards leaf tip.
Fissidens dubius Note:
Irregularly toothed towards leaf tip.
Hylocomium splendens
Hyocomium armoricum
Isothecium alopecuroides Note:
Teeth only present towards the tip of the leaves.
Kindbergia praelonga
Mnium hornum
Oligotrichum hercynicum Note:
Widely spaced.
Palustriella commutata Note:
Denticulate below (and possibly throughout).
Philonotis fontana
Plagiomnium ellipticum Note:
Sometimes lacking.
Plagiomnium rostratum

Plagiomnium rostratum (Mniaceae)

Teeth on leaf margins

Marginal teeth in moss leaves are often unicellular, comprising a cell with a projecting corner as seen here in Plagiomnium rostratum. Note also the difference between the marginal border cells and those behind the leaf margin.

Plagiomnium undulatum
Pogonatum aloides
Pogonatum urnigerum
Pseudoscleropodium purum Note:
"Lightly toothed" according to Watson, although I've not yet noted the teeth.
Pterygonium gracile Note:
Dentate above.
Ptychomitrium polyphyllum
Rhynchostegium confertum
Rhodobryum roseum Note:
Distantly toothed at apex.
Rhytidiadelphus loreus
Rhytidiadelphus squarrosus
Rhytidiadelphus triquetris
Thamnobryum alopecurum Note:
At apex.

While compiling this list I noted that many mosses with teeth, bear them towards the leaf tip only, and so a separate list of these might be helpful. A further discrimination could be made in relation to the shape (e.g. sharp, blunt), spacing and relative size of the teeth (including whether they are multicellular).

Teeth on hairpoints only

Polytrichum piliferum
Campylopus atrovirens
Grimmia pulvinata Note:
Lightly but distinctly toothed.
Hedwigia stellata Note:
Hyaline apex bears spinose teeth.
Racomitrium lanuginosum
Syntrichia ruralis ssp. ruraliformis

Grimmia pulvinata (Grimmiaceae)

Teeth on hairpoints only

The characteristic form of toothed hairpoints is illustrated by these leaves of Grimmia pulvinata, the teeth comprising out-turned extensions of the long hyaline cells comprising the hairpoint.

The teeth on hairpoints and hyaline tips of moss leaves, often have an appearance quite different from the kinds of teeth that are borne on leaf margins. In the latter, it's common for a marginal cell to be triangular or with a distinct kink, such that a tooth-like projection is formed. The teeth on hyaline points, on the other hand, often look like spinose projections of cell wall material.

Teeth absent

Amblystegium serpens
Amphidium mougeotii
Aulacomnium androgynum
Barbula convoluta
Barbula unguiculata
Brachythecium albicans
Bryum alpinum
Bryum argenteum
Bryum capillare
Bryum pallens
Bryum pseudotriquetrum
Calliergon giganteum
Calliergonella cuspidata
Campylopus introflexus
Ceratodon purpureus
Dichodontium palustre
Dicranoweisia cirrata
Didymodon rigidulus
Fissidens bryoides
Funaria hygrometrica
Grimmia laevigata
Gymnostomum aeruginosum
Gyroweisia tenuis
Homalothecium sericeum
Hypnum andoi
Hypnum jutlandicum
Neckera complanata
Neckera crispa
Orthotrichum anomalum
Plagiothecium undulatum
Pleurozium schreberi
Pohlia melanodon

Amphidium mougeotii (Rhabdoweisiaceae)

Absence of teeth on leaf margins

Marginal teeth on moss leaves can be more or less conspicuous, but in Amphidium mougeotii, the leaf margins are decidedly plane.

Pohlia nutans
Pseudocrossidium hornschuchianum
Pseudocrossidium revolutum
Racomitrium aciculare
Racomitrium fasciculare
Racomitrium heterostichum
Rhizomnium punctatum
Schistidium maritimum
Schistidium rivulare
Syntrichia laevipila
Tortella tortuosa
Tortula muralis
Trichostomum brachydontium
Ulota bruchii
Ulota phyllantha
Warnstorfia fluitans

The cursory investigation made here suggests that there's as many moss species with marginal teeth as without.

Details of the leaves character table View these data from a taxonomic viewpoint with notes on substrate and habitat (Class Bryopsida only)

Go to:
Bryophyte introduction

Go to:
Plant growth habit

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Shoot growth form / colour

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Arrangement of the leaves

Details of the leaves lists

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Reproductive structures

Go to:
Summary

The moss line