To begin with, we look at a few mosses commonly found on walls,
especially walls containing basic rocks.
(Wall Screw-moss) (Pottiales)
Above and below: Tortula muralis. This is one of the easiest mosses for beginners to find. This moss is autoicous (autoecious) meaning that male and female organs are in separate clusters on the same plant. When dry the leaves press and twist together, but spread out when moist. Each leaf ends in a whitish translucent hyaline hair. This moss is acrocarpous: forming erect shoots which may end in the reproductive organs and sporophyte (seta + capsule).
The capsule of Tortula muralis is narrow and cylindrical.this moss consists of small cushions (less than 1 cm tall) of upright shoots, each of which may bear a terminal seta and spore capsule (it is an acrocarpous moss). The peristome teeth are long fibers that twist together when moist, closing the capsule ( a hygroscopic lid) but untwist to open the capsule in dry conditions, to allow wind to shake free the spores for dispersal. This spiral closing of the capsule in damp conditions gives the genus its name of Tortula (the Screw Mosses). External link: http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmar03/dcmoss.html.
The leaves (or phyllids as moss leaves are sometimes called) spread out when moist and turgid, but twist together when dry. Like many mosses they can survive desiccation and revive when moisture returns. Being small plants without the waxy water-proofing cuticles and other adaptations that the leaves of flowering plants have, mosses can not easily retain their water content in dry conditions and so must tolerate periodic desiccation or exist in permanently wet environments. The central nerve of each leaf extends as a silvery hairlike projection from the leaf tip.
Grimmia pulvinata (Grey-cushioned
This is the most common species of the genus Grimmia with an almost global distribution and is particularly common in Britain and on the west coast of North America. It forms round cushions 1 to 2 cm tall. Each leaf bears a silvery hairlike extension at the tip. Grimmia is also autoicous and acrocarpous.
The capsules (below) are cylindrical with distinct longitudinal lines and a very beaked cap (calyptra). The seta recurves (bends back on itself) so that the capsules lie buried within the leaves, but straighten in old and dry mosses to facilitate spore dispersal.
Grimmia pulvinata is a xerophytic moss (adapted to dry conditions) and in experiments it has survived 60 weeks in a desiccator to be revived upon rehydration. This moss grows on basic rocks, including walls and is fairly resistant to pollution so is characteristic of urban environments. It may occasionally be found growing on the bark of woody plants. The capsule has apparent air spaces within it for photosynthesis. The capsules of Grimmia pulvinata have characteristic longitudinal lines and when dry they can be seen to possess 8 longitudinal ribs.
Grimmia pulvinata is a xerophytic moss, meaning that it can tolerate dry conditions, or more specifically periodic drying out. Mosses have differing resistance to desiccation: aquatic mosses like Fontinalis squamosa, which grows in streams and rivers attached to rocks and tree roots, will frequently be unable to recover after a week of air-drying, whilst Grimmia pulvinata has been known to withstand sixty weeks in a desiccator at 20 degrees C (Watson, E. V. 1964 The Structure and Life of Bryophytes, Hutchinson University Library). Thus, the apparently miraculous ability of mosses to revive upon rehydration has its limits and so some mosses have adaptations to reduce the severity of drying out, such as the folding or twisting up of leaves as they dry, although the benefits of thsi are not clear: it possibly helps the moss retain the last drop of water for longer, or protects the brittle dry leaf from mechanical damage or perhaps speeds up water transport by capillary action once water becomes available again. The hair-like (excurrent) extensions of the nerves at the leaf tips is also thought to be a xerophytic adaptation, though the function of such appendages is not clear (I suggest that they may serve to conserve moisture by increasing boundary layer thickness).
The adaptations of xerophytic mosses has been reviewed by Watson, W (New Phytologist, 1914). Tortula muralis is also xerophytic. These include the formation of dense cushions, to retain moisture, as in Grimmia and Tortula Clearly resistance to periodic drying is a useful adaptation for wall-dwelling mosses. Forms of Tortula growing on damp walls may have longer setae when growing on damp walls, presumably to position ripe capsules in the drier air for spore dispersal.
The photo below shows Grimmia pulvinata growing alongside what appears to be Tortula muralis in the hydrated state (with leaves expanded). Note the terminal cups of leaves, these are the perichaetia (sing. perichaetium) consisting of a circle of perichaetial leaves or bracts (which are more or less modified in different mosses) enclosing the female reproductive organs. (A perichaetium encloses either both male or female organs or female organs only, a perigonium of perigonial leaves encloses male organs only).
recurvirostrum ( = Barbula recurvirostrum, Red
This moss grows on basic rocks, including walls, and thin calcareous soil and sometimes in tree boles on flood plains near streams and rivers. It belongs to the order Pottiales. It forms loose turfs / sheets and is up to 5 cm tall. The lower leaves often have a reddish color in which case this is a distinguishing feature. The leaf margins also fold inwards.
The cylindrical capsules are held upright on a seta that is often reddish in color, especially in its lower parts.
This moss has both male and female organs borne on the same plant, typically interspersed on the same cluster or inflorescence (synoicous) sometimes with the male antheridia naked in the axils of the bracts (modified leaves surrounding reproductive organs) - a condition called paroicous.
crassipilum (Thickpoint Grimmia) (Grimmiales)
Above: Schistidium crassipilum (bottom left of center) growing
with Grimmia pulvinata and Tortula muralis. This plant
is common on walls and tarmac (here on a concrete rock) but can also be
found on limestone and basic sandstone rocks.
In Schistidium the capsules remain enclosed by modified leaves with just their tops showing (they are immersed in the perichaetial leaves that surround the female reproductive organs from which the capsules spring). This moss is auoicous and has no or few stomata on its capsules. The immersion of the capsules and the lack of stomatal pores upon it are again adaptations for dry conditions: protecting developing spore-generating tissues from excessive dehydration (once mature the capsules may dry to release the spores that are generally more resistant to dry conditions and indeed more easily dispersed in dry air). In mosses in general, the capsule usually contains between 3 and 200 stomata, presumably to facilitate photosynthesis which occurs in the developing capsule and presumably provides the sporophyte with some of its resources for spore production. These stomata are largely insensitive but will close when the capsule is very dehydrated.
Common Mosses from an Ash-Beech-Hornbeam Wood
(Common Feather-moss) - Hypnales
Kindbergia praelonga is a moss belonging to the order Hypnales and there are about 7 species in the Kindbergia genus. It forms shoots, up to 3 cm long, that branch either side in a plane (pinnate branching as in a fern leaf) with a feather-like appearance. This moss typically ascends the trunks and branches of trees or grows on the woodland floor and over logs. It is most common in lowland woods. Do bear in mind that some moss species are rare and so no materials should be collected if in doubt and minimal materials needed for identification should only be collected from large populations.
The capsules are ovate, inclined to horizontal and borne on reddish seta which are usually distinctly roughened (paillose) in Kindbergia. The capsules have a beaked lid (operculum), which is quite characteristic of the Hypnales which have conical to beaked lids. The perichaetial leaves (those surrounding the female reproductive organs and hence the seta, in a cup-like fashion) also end in a fine hair-like tip (acumen) which is characteristic of this genus.
The peristome of Kindbergia praelonga is perfect, meaning that it has the full complement of 16 outer and 16 inner peristome teeth.
Above: the calyptra is still enclosing the operculum (lid) of this moss capsule.
Characteristic of Kindbergia praelonga is the differing shapes of stem and branch leaves. Stem leaves, seen above, have a wide base flaring out, whilst branch leaves (below) have much narrower bases.
(Common Smoothcap / Catherine's Moss) - Polytrichales
Atrichum undulatum belongs to the order Polytrichales.This moss has characteristically undulating leaves (as does Plagiomnium-undulatum which also grows in this locale, see below). it is a large moss with erect acrocarpous shoots reaching 7 cm in height. It is found in lowland woods (as well as heaths, grassland, anthills, rocky ledges) and prefers approximately neutral substrates.
The conspicuous capsules of A. undulatum are held in an almost horizontal position on seta up to 3 cm long and are curved or arcuate (arc-shaped) with a very long beak on the operculum (lid). this is probably var. undulatum in which capsules are common.
Below:characteristic of this moss (distinguishing it from Plagiomnium-undulatum) are the curious longitudinal plates or sheets of cells (lamellae) that lie along the nerve of the leaf.
Below: the perichaetial leaves of Atrichum are generally longer and narrower than the stem leaves.
(Hart's-tongue Thyme-moss) - Bryales
Plagiomnium undulatum belongs to the order of mosses: Bryales.Like Atrichum undulatum it also has undulating leaves, but the leaves have much blunter tips and the moss can reach a larger size, with shoots up to 15 cm long and which show tree-like branching. its nerves also lack the longitudinal lamellae found in Atrichum undulatum. It grows in neutral to basic woodland soils and grassland.
P. undulatum can reproduce asexually by means of stolon-like shoots. The moss is dioicous (the male antheridia and female archegonia are borne on different plants).
(Cypress-leaved Plait-moss) - Hypnales
This pleurocarpous moss belongs to the order Hypnales and typically forms prostrate branching shoots up to 8 cm long. Its capsules have beaked lids. It is very common on bark and siliceous rocks, preferring acidic, neutral and slightly basic substrates. There are about 22 species in the genus Hypnum.
Above: the leaves of Hypnum cupressiforme either lack nerves or have very short double nerves and have long tapered and curved tips characteristic of the genus. Another similar species is Hypnum jutlandicum (Heath Plait-moss) but based on the habitat H. cupressiforme is the more likely species here. The sporophytes (sporophyte = seta + capsules) have become detached 9along with perichaetial leaves) from their parent plant and so we can not be certain that they are capsules of H. cupressiforme, though they have the right general morphology and probably are (but those of Isothecium are also similar though are some differences under close microscopical examination). Note the detached capsule lid (lower left in the above).
formosum (Bank Haircap) - Polytrichales
Polytrichastrum formosum (Bank Haircap, formerly Polytrichum formosum)is superficially similar to Polytrichum commune but the former grows in drier habitats and its capsules lack a basal constriction. The capsules of both species are box-like with well formed angles (4-angled in Polytrichum commune, 5 to 6 angled in Polytrichastrum formosum) with beaked lids. The beak is longer in Polytrichastrum formosum and the seta shorter. Microscopically, the leaves of these two species can be distinguished.
The leaves of Polytrichastrum formosum (shown here) and Polytrichum commune have close-packed longitudinal columns of photosynthetic cells covering the adaxial (front) of the leaf, but in Polytrichastrum the leaf is flatter with a v-shaped protruding nerve on the back, whereas the backs of the leaves of Polytichum are distinctly rounded.
Polytrichastrum commune occurs in deciduous woodland, both lowland and upland on acidic soils and heaths. Polytrichum commune occurs in wetter places of similar habitats (including bogs).
(Swan's-neck Thyme-moss) - Bryales
There are some 19 species in the genus Mnium. Mnium hornum is one of the most common mosses of the British Isles, but is also found in other parts of Europe, Africa, Asia, North and South America. When mature, the seta curves over, leaving the capsule pendant, but still clearly emergent from the leaves, hence the name of 'Swan's-neck'.
The leaves have characteristic borders, which are strongly developed and minutely toothed.
Above:a male 'flower' of Mnium hornum. Mosses do not have true flowers, but the sex organs are often in groups and surrounded by modified leaves (perigonial leaves surround groups of male organs, perichaetial leaves surround female organs or mixed groups of both male and female). The purpose of these perigonial leaves is to catch and retain water, since water is required for the release and motility of the male antherozoids (sperm cells). The male organs (antheridia) are embedded in a mass of sterile orange hair-like structures called paraphyses (visible in this case).
rutabulum (Rough-stalked feather-moss)
The picture above shows a variety of mosses (how many distinct types can you see?) including some we have already discussed, but there is at least one other species: two distinctive plants visible in the top half of the image with distinct leafy shoots, which almost look like little flowering plants. These are probably mosses of the Plagiomnium genus of similar species. Ample Plagiomnium undulatum grows in this area and perhaps these are very young plants of this species, or a different species such as Plagiomnium affine. A closer look is required to be certain.
The dark red capsules with conical lids are borne on roughened seta and almost certainly belong to a species of Brachythecium (Feather-moss). A close inspection of the leaves will enable the species to be determined (the prime candidates are Brachythecium rutabulum, B. populeum and B. velutinum. A closer follow-up inspection revealed this to be Brachythecium rutabulum (Rough-stalked Feather-moss). The irregular branches of this moss are ascending/erect.
haracteristic of Brachythecium rutabulum, the egg-shaped and slightly curved capsules are dark color and similar in color to the red seta when mature and held inclined to horizontal (sometimes hanging-down or 'pendant'). The seta is characteristically papillose (warty).
The egg-shaped leaves have nerves that end well below the tip. This moss is very common in the British Isles, and is also found in other parts of Europe, North and Central America, n. Africa and Oceania. grows on soil, wood, stones, walls, tree trunks and branches, logs and stumps in both shaded and open areas.
Article created: Jan 2020
Article updated: 21 Jan 2020