The majority of the rocks in Wales are acidic in nature, and this is reflected in bryophyte species that grow on them. Different species may occur where the rocks are more base-rich (carboniferous limestone,for example)

Man-made walls are also often dry and inhospitable to many higher plants, and of course they are often made of natural stone. Many of the bryophyte species found on natural rocks are also found on walls, and again the nature of the rocks, and any mortar used will influence the species that grow on them.

Some of the mosses and liverworts that grow on rocks and walls in Wales are listed below:

Mosses

Bartramia stricta

This is a drought-tolerant moss occurring on rock and soil on South-facing slopes. Common in Mediterranean regions, it has only ever been recorded at 4 sites in the UK, two of these in Wales. The population at one of the Welsh sites (Breidden Hill in Montgomeryshire) is now almost certainly extinct, destroyed by quarrying. Pale to bright green in colour, its leaves are long and tapering to fine points, with toothed margins in the upper part. Its capsules are globose and highly symmetrical. It is closely related to the much commoner Bartramia pomiformis, which differs in its asymetrical capsules.

Blindia acuta

A frequent moss on wet rock ledges in the uplands of Wales, as well as on small rocks in flushes or rivulets. The leaves are a dull green in colour, are rather small and narrow, tapering to fine points. It has a stong midrib, and under the microscope, or even the hand-lens, patches of orange-brown cells are visible on either side of the base of the nerve.

Campylopus setifolius

This is an oceanic species, confined to the West and North of Britain. It occurs on acid rocks in a number of well-drained, humid situations in North Wales, including N-facing crags, crevices of shaded block scree, and in the spray zone of waterfalls. In common with other species of Campylopus it has long, narrow leaves tapering to fine points, and a very thick nerve occupying most of the leaf width. The upper quarter of the leaf has spiny teeth at its margin, and the plant is mid- to dark green in colour. The species is Nationally Scarce, and near endemic - outside Britain it is only known from N.Spain.

Coscinodon cribrosus

This moss grows in cushions on very acidic slate or shale in dry, exposed situations. Its leaves are have nerves which extend beyond the leaf tip top form a conspicuous hair-point. On either side of the nerve the leaves are folded in longitudinal furrows.

Orthotrichum anomalum

This is the commonest rock species of Orthotrichum and grows on base-rich rocks (such as Carboniferous limestone) and artificial walls, buttresses etc., usually in exposed situations. It forms neat dark-green cushions with abundant capsules projecting only a little distance from the cushions, on short setae. The leaves are wide toward the base, tapering gently to an obtuse tip, with a small point, or apiculus. The nerve is strong, and runs for most of the leaf length.

Racomitrium aciculare

A common species which occurs as green or blackish tufts on rocks which are periodically wet, most often beside streams and rivers, and in open or only partly-shaded situations.

Racomitrium lanuginosum

A common species on boulders and rock outcrops in the Welsh uplands, as well as on peat hags in eroded blanket bogs, and numerous other habitats. The shoots are greyish-green in colour, and conspicuous by their long white hair points, giving the plants a somewhat woolly appearance.

Scorpiurium circinatum.

This moss occurs on limestone rocks and walls at scattered locations on the South coast of Wales, and on the coast of the island of Anglesey in the North. It is a Mediterranean species and is at its northern limit in the British Isles, where it is classified as Nationally Scarce. Its leaves are triangular, with a strong nerve and a toothed margin. They are closely adpressed to the stem (imbricate) when dry (see inset) but spreading when wet,so that the plant has a quite different appearance in each of these states.

Tortula muralis

A moss very commonly found on brick and stone walls in all parts of Wales, even in the cities. It is conspicuous when with capsules, which are narrow and erect on setae which are yellow when young later turning purplish-brown. The leaves are tongue-shaped, with a nerve that extends in a silvery hair point, and recurved (folded-down) margins.

Liverworts

Gymnomitrion crenulatum

Similar to Gymnomitrion obtusum, but usually a copper red-brown in colour, and with acute-tipped leaf lobes. This species also occurs on boulders and rock outcrops.

Gymnomitrion obtusum

This liverwort is usually conspicuous on rock ledges and boulders in the uplands of Wales. It forms distinct cushions or mats which are pale yellow-green to almost white in colour. The leaves are rounded, with two shallow, obtuse lobes and are tightly overlapping, giving an almost cylindrical appearance to individual shoots.

Marchesinia mackii

Olive-green to almost black in colour this leafy liverwort occurs on shaded, more or less vertical, basic rocks. The leaves are closely spaced and overlapping ("imbricate"), and the shoots are closely adpressed to the substrate.