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Moss characters
Reproductive structures
Character menu
The character categories and their possible forms are:

Asexual reproduction in mosses
The many ways mosses propagate themselves

Mosses have evolved a surprising variety of means of vegetative reproduction, where some part or structure of the gametophytic plant is released from the parent to establish further individual plants.

The reproductive propagules range from deciduous shoots which simply break off the parent (as in species of Campylopus), to various sorts of gemmae and tubers comprising clumps of cells which have resources to help establish new plants when they reach a suitable substrate and environment. Gemmae can be carried aloft by special structures, or just distributed on some part of leaf surfaces, while tubers can be found in the soil amongst the rhizoids which play a root-like role for the gametophyte above.

Deciduous shoots
?Campylopus sp.

In many species of Campylopus, the shoots are fragile and readily separate from the parent plant to act as vegetative propagules. Moss photographed at Rubha nan Sasan, Loch Ewe in the Scottish Highlands. (ID tentative)

Sexual reproduction in mosses
The cycle of generations

Sexual reproduction in mosses takes place when male and female haploid gametes come together to form the diploid sporophyte. The gametes are produced on a variety of structures on the green leafy plant, both sexes sometimes occuring on one individual, while other species have separate male and female plants.

After fertilisation, the diploid plant or sporophyte is formed, comprising a haustoria-like foot embedded in the gametophyte plant body, from which extends the seta or stalk surmounted by the capsule. Meiosis takes place in the capsule to produce large numbers of tiny haploid spores. After dispersal, spores landing on a suitable substrate germinate, forming a green thread-like plant body called a protonema which is reminiscent of a green alga. The leafy gametophytic plant arises from the protonema and the cycle continues.

Moss protonema
Dicranella rufescens protonema

The green mat formed by the protonema that gave rise to the leafy and capsule-bearing mature moss, can be seen in this picture of Dicranella rufescens. On bare soil in a drainage ditch near Daer Reservoir, South Lanarkshire.

The calyptra
Polytrichum piliferum

Young sporophytes on Polytrichum piliferum made very conspicuous by the bright orange calyptra on each capsule. In mosses, the seta begins to elongate before the capsule is mature, a fragment of the female repoductive organ (the calyptra) being ruptured from the haploid plant and carried aloft. Experiments have shown that the calyptra is required for normal capsule development. As the capsule matures and expands in P. piliferum, the calyptra appears more pale in colour due to the development of copious hairs.

Photographed growing on rocky soil on Arthur's Seat, Edinburgh.

Internet sites
Peristome teeth
Mnium hornum capsule

At the mouth of the capsule in many mosses, spore release is regulated by hygroscopic peristome teeth. Although the number and structure of peristome teeth is an important phylogenetic character, I haven't seen it much used as a field character, presumably as it requires microscopic examination. However, the peristome teeth on this capsule of Mnium hornum can be clearly seen even with modest magnification.

Many characters
More to do...

The background research I've carried out to put together these character lists for the more common mosses found in the UK, has highlighted for me just how many characters exist in mosses. Mosses are obviously less structurally differentiated than flowering plants, but within the small range of tissus they possess, there's an amazing variety of form. Indeed, if mosses were much larger, or we were much smaller, we would be surprised at the diversity in geometric form shown by moss shoots and leaves.

In these pages I've covered some of the more conspicuous characters with an emphasis on those that can be observed with no more magnification than a x20 hand lens. But even at these scales, there are many details of leaf and capsule form, for example, that could be added here with the associated species.

It's my intention to revisit these lists from time to time, adding further species to the lists as well as enhancing the content by including further morphological and anatomical characters.

Gemmae forming a ball on the ends of shoots
  • Aulacomnium androgynum
Aulacomnium androgynum Aulacomnium androgynum (Aulacomniaceae)

Aulacomnium androgynum

Gemmae on "stalks"

When Aulacomnium androgynum is bearing gemmae, it's a very distinctive and easily-identified moss.

The balls of gemmae borne at the tops of bare shoots have some resemblance to the gemmiferous projections and spheroidal masses of gemmae seen in the liverwort Blasia pusilla.

I'll be researching into whether similar gemmae-bearing structures occur in other mosses in Britain and Ireland, but for now I list the only species I know with this structure.

Gemmae forming a clump on the tips of leaves
  • Ulota phyllantha
Ulota phyllantha Ulota phyllantha (Orthotrichaceae)

Ulota phyllantha

Gemmae on tips of leaves

I'm sure there's more than one moss species with gemmae on the leaves, but I encounter Ulota phyllantha frequently, and its gemmae are borne in such abundance that the plant looks as though covered in dust or soil particles.

I find it intriguing that mosses can bear gemmae in various parts of the plant, including on the tips of the leaves in the case of Ulota phyllantha. The implication seems to be that moss tissues and organs retain a fairly open developmental pathway, rather than their cells being committed to performing a limited series of roles.

Flower-like perigonial shoots
  • Polytrichum juniperinum
  • Polytrichum piliferum
Polytrichum juniperinum Polytrichum juniperinum (Polytrichaceae)

Polytrichum juniperinum

Flower-like perigonial shoots

The antherozoids are protected beneath the overlapping inner leaves at the top of this male shoot of Polytrichum juniperinum.

The sexes in Polytrichum gametophytes are separate, and the sperm or antherozoids develop in antheridia that are borne below enlarged leaves on the male plants. These perigonial leaves form part of a cup-like structure which enhances the dispersal of the antheridia through a splash-cup mechanism.

The position of the "cup" at the top of an erect shoot contributes to the surprisingly flower-like appearance, as the photo of a male gemetophytic plant of Polytrichum juniperinum shows.

Seta yellow
  • Atrichum undulatum
  • Brachythecium plumosum
  • Bryum capillare*
  • Dicranoweisia cirrata
  • Tortula muralis*
  • Ulota bruchii
  • Weissia controversa*
Ulota bruchii Ulota bruchii (Orthotrichaceae)

Ulota bruchii

Seta yellow

Ulota bruchii has a green patch of photosynthetic tissue between the yellow seta and the capsule.

In mosses, the diploid sporophyte is dependent on the gametophytic plant for much of its water, nutrient and photosynthate resources. But just below the capsule in many species, there is a patch of green photosynthetic tissue (with stomata) showing that the sporophyte can manufacture at least some of its own sugars.

Seta orange
  • Brachythecium rutabulum
  • Bryum capillare*
  • Bartramia pomiformis
  • Mnium hornum*
  • Tetraplodon mnioides
  • Weissia controversa*
Brachythecium rutabulum Brachythecium rutabulum (Brachytheciaceae)

Brachythecium rutabulum

Seta orange

The seta in the specimen of Brachythecium rutabulum here is a rich orange colour.

The precise colour of the seta is perhaps an unreliable diagnostic in itself beacause a species may show a colour range, and it's not always easy to judge when a red could be considered orange, yellow a light green, and so on, especially in different lighting conditions. However, it is a conspicuous character, and it might be possible to discount a considered identity when the seta in the latter species is a colour very different from that in the specimen being studied.

Seta red
  • Bryum argenteum
  • Brachythecium populeum
  • Ceratodon purpureus
  • Rhizomnium punctatum
  • Tetraplodon mnioides
Ceratodon purpureus Ceratodon purpureus (Ditrichaceae)

Ceratodon purpureus

Seta red

This fertile specimen of Ceratodon purpureus illustrates an issue with seta colour as a diagnostic - the colour varies from red at the base to yellow towards the base of the capsule.

When Ceratodon purpureus is fertile, it often bears abundant sporophytes which obscure the diminutive gametophytic plant. In late afternoon sunlight in winter, the red (or even purple-red) setae give tufts of this moss a warm glow.

Seta brown
  • Amblystegium serpens
  • Bryum capillare*
  • Eurhynchium striatum
  • Mnium hornum*
  • Pogonatum aloides
  • Rhynchostegium confertum
  • Tortula muralis*
Rhynchostegium confertum Rhynchostegium confertum (Brachytheciaceae)

Rhynchostegium confertum

Seta brown

The slightly twisted brown setae in Rhynchostegium confertum appear almost woody in this image.

It's possible that the setae in a number of moss species develop a brown coloration with age, and I don't know at present whether those of Rhynchostegium confertum are brown all through their development.

Capsule opening by four splits
  • Andreaea spp.
Andreaea sp. Andreaea sp. (Andreaeaceae)

Andreaea sp.

Four splits

The splitting of the capsules of Andreaea species creates a Chinese lantern appearance. This specimen was growing on a boulder at the foot of Loudoun Hill, Ayrshire.

The unique capsule of species of Andreaea is unmistakable, the capsule wall opening by four longitudinal splits at maturity. It's interesting to note the similarity with the way liverwort capsules split into four valves to release their spores.

Capsule opening by apical pore
  • Sphagnum spp.
Sphagnum subnitens Sphagnum subnitens (Sphagnaceae)

Sphagnum subnitens

Apical pore

This focus-stacked image of Sphagnum subnitens shows the apical pore on the capsules. Note that the capsule sits on a pseudopodium, i.e. an elongated growth of the gametophyte.

The capsules in Sphagnum mosses do not have peristome teeth at their apex, but instead a circular line of weakness allows a "lid" to pop off at maturity. .

Capsule drooping on long seta
  • Bryum capillare
  • Mnium hornum
Bryum capillare Bryum capillare (Bryaceae)

Bryum capillare

Drooping capsules

Bryum capillare is a small moss with its drooping capsules borne on a relatively long seta.

Drooping capsules are typical of Bryum species. Having a long seta must be an important feature for mosses whose capsule remains downward-pointing at maturity, so that the spores can be caught by air currents as they fall towards the ground.

Mature capsule very thin
  • Tortula muralis
Tortula muralis Tortula muralis (Pottiaceae)

Tortula muralis

Thin capsules

This small tuft of Tortula muralis shows mature capsules which are small in diameter in relation to their length.

This character could be misleading if care is not taken to ensure that the capsules are thin yet mature. Note that in mosses the seta completes its elongation while the capsule is still immature and the latter has not yet expanded.

Capsule distinctly spherical
  • Bartramia pomiformis
Bartramia pomiformis Bartramia pomiformis (Bartramiaceae)

Bartramia pomiformis

Spherical capsules

The young capsules on this specimen of Bartramia pomiformis do look like the apples referred to in the specific name.

While young capsules of Bartramia pomiformis are quite spherical, older ones become somewhat elongate.

Capsule shaped like an ampule
  • Tetraplodon mnioides
Tetraplodon mnioides Tetraplodon mnioides (Splachnaceae)

Tetraplodon mnioides

Ampule-shaped capsules

Tetraplodon mnioides typically grows on decaying animal remains, a substrate sufficiently unique, that combined with the unusual capsules should lead to a confident identification.

Ampule-shaped capsules, like those of Tetraplodon mnioides, are a characteristic feature of species in the Splachnaceae. The peristome teeth are large and fold back, the yellow attached sticky spores contributing to an appearance like an anther covered in pollen.

Epiphragm present
  • Pogonatum aloides
Pogonatum aloides Pogonatum aloides (Polytrichaceae)

Pogonatum aloides


The bright-white epiphragm in Pogonatum aloides is very conspicuous, even in the field.

Many mosses have peristome teeth at the mouth of the capsule, between which spores can escape. In Pogonatum aloides and other members of the Polytrichales, in place of a peristome is a membrane (the epiphragm) with holes around its circumference. The spores escape like salt from a salt shaker.

Capsule immersed
  • Orthotrichum rivulare
  • Schistidium spp.
Orthotrichum rivulare Orthotrichum rivulare (Orthotrichaceae)

Orthotrichum rivulare

Capsule immersed

The large capsule of Orthotrichum rivulare is embedded in the leafy shoot, hiding the short seta.

Many species of Orthotrichum grow as epiphytes on trees, and so short setas could be considered adequate for spore dispersal due to the moss's elevated position. However, Ulota species share a similar niche and have long setae. Furthermore, Orthotrichum rivulare grows attached to rocks by running water, and it might be thought that spore dispersal could have been more efficient with long setae.

I think this illustrates that speculation over the adaptive significance of characters can be suspect, and counter evidence should always be considered.
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