Because of their high nutrient content, and high pH, rich fens are usually dominated by vascular (mostly flowering) plants - the photograph shows an example of this type of fen. Many of the bryophytes that are occur are mosses with some brown colouration, and they are often referred to collectively as the "brown mosses" (see below for examples). Poor fens are closer to bogs in pH and nutrient availability, and share some species with bogs. They tend to be dominated by mosses, including Sphagnum mosses (some of the Sphagnum mosses that occur in fens are never found in acidic bogs, and can be good indicators of a higher pH. They may occur in base-rich flushes amongst predominantly acid conditions).

Much fenland has been drained and claimed for agriculture over the years, and many of the bryophytes associated with fens are now uncommon.

The table below summarises some of the characteristics of rich and poor fens:

Some of the mosses and liverworts to be found in fens in Wales are:

Mosses

Cratoneuron commutatum

When well-grown this is a distinctive moss, with its rich golden-yellow to orange-brown colouring (it counts as one of the "brown mosses") and regular pinnate branching. A notable feature is the coat (tomentum) of thick reddish-brown rhizoids (or radicles) which often clothe the lower parts of the stem. The leaves are longly tapering to pointed tips, and curved round like a sickle. They have a nerve running their length and distinct auricles at their basal corners. Two varieties are recognised: var. commutatum and var. falcatum. They occupy somewhat different ecological niches but always occur where calcium is present in significant amounts.

Drepanocladus exannulatus

This moss has a rather feathery appearance, is a golden- yellow to pale brown colour. Its leaves are long and tapering to a fine point, slightly curved, with a nerve running for most of their length, and pronounced auricles in their basal corners. In common with other species of Drepancocladus the leaves tend to be orientated in the same direction away from the stem (a condition known as secund). This is a plant of open poor fens and flushes as well as the edges of mildly acid lakes and ponds.

Drepanocladus revolvens

This species is marked by its long, tapered leaves, which are strongly curled around to the extent of almost forming a circle. The leaves are orientated to one side of the stem (secund). It is a robust plant and is usually tinged with orange, crimson or purple, mixed with yellowish-green (it may be confused with Scorpidium scorpioides, with which it often grows). Found in mildly to strongly base-rich flushes and fens with a pH above 6.0.

Rhizomnium punctatum

This is a robust erect-growing moss, with a very characteristic appearance. Its leaves are broad, with a thickened border, and a distinct nerve running their entire length. The plant is a glossy deep-green in colour. The lower parts of the stems are matted with a red-brown tomentum.

Scorpidium scorpiodes

A moss often found in wet, base-rich flushes, frequently with Drepanocladus revolvens (with which small forms can be confused). It is usually robust, with a swollen appearance, and coloured purple or dark red, going to almost black in its lower parts. The leaves are wide, concave in the middle, tapering abruptly to a short point. They are wrinkled, and usually have only a very short, forked nerve.

Sphagnum subsecundum

This Sphagnum moss is predominantly a rich brown to golden-yellow in colour and thereby readily distinguished from many other species of the same genus. It is found in flushes and poor fens, sometimes in swamps, but never in very acid conditions. In the UK it is Nationally Scarce, but it is likely to be underrecorded due to previous confusion with the related Sphagnum auriculatum var. inundatum.

Liverworts

Aneura pinguis

This is a thallose liverwort that occurs in dune-slacks, fens and flushes, and other moderately base-rich habitats. Bright or deep green in colour, it is irregularly branched with branches concave and some 2-3 cm in length and 2-6 mm wide. Branches are thickened in the middle, with thinner margins, which may be somewhat wavy in outline. It tends to be brittle, and have a rather greasy appearance. May be confused with Pellia species, but the tips of the lobes in Aneura are entire, whilst in Pellia they are emarginate.

Preissia quadrata

This is a thallose liverwort, generally a pale green in colour with red-brown or purplish margins, and its branches up to 1cm wide. The upper surface of the thallus has hexagonal markings and at the centre of each hexagon is a small pore. This liverwort is a strong calcicole and is found on a wide variety of basic substrates, including soil in calcareous fens and flushes, stream-banks, moist or dry rocks and cliffs, on the crumbling mortar of walls, as well as in dune-slacks.

Riccardia multifida

A very slender liverwort with a finely branching thallus, each branch being only about 0.5mm in width. The edges of the branches are only one cell thick and transparent, and although thicker at the middle, there is no clearly-defined midrib. It has a wide range of pH tolerance and can occur in both rich and poor fens, as well as a variety of other habitats, including lake margins, wet soil in woods, and tracks.