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Life in Freshwater

Mosses

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(Foninalis antipyretica)
Willow Moss (Foninalis antipyretica) with caddisfly adult

There are several moss species which can be found living and adapted to water. There are surprisingly few species for an environment that could be ideal. THis is because mosses are relatively primitive with little ability to support themselves so that they could grow tall. This is why on land they are limited to damp places where they rarely grow more than a few centimetres. Here water will give that support. Not surprisingly then, we see the largest species of moss growing in slow moving sections of rivers and also ponds/lakes. This is the Willow Moss (Foninalis antipyretica) and will grow in long strings with occasional forks. The leaflets are dark green (to absorb maximum light across the spectrum when under water) and keeled. The name is derived from the fact that it was used in the past as a fire retardant by nomads in Lapland.

Another long stringy species is Eurhynchium riparoides which attaches to stones and wood found in fast flowing water. The older, darker parts of the plant are devoid of leaflets and may be very tough to prevent being ripped away by the current. The younger sections have pale green leaflets for photosynthesis. Other specie sof this genus live on land.

The Sphagnum mosses or Bog Moss is prolific in wet areas of the north and west Britain. Typically upland and damp, acidic lowland areas. They live in still water only, especially moorland pools or at the bottom of valleys. There are many species and it would be difficult to give a detailed breakdown here.

The Sphagnum mosses or Bog Moss

Bog Moss

Most form dense bunches of leaflets attached to a stalk. All are primitive plants with no vascular or conducting tissue. They grow from the upper stalk, dying at the base. The leaflets have small pores in them allowing the entry of water such that they hold it like a sponge. The following are common species:

S. capillifolium is a dark red/brown with tinges of pink and green. Common in the north and west it grows in dryer areas of a bog, under heathers or on top of hummocks. S. papillosum is yellow with green and brown patches. Common on most bogs it grows in damp areas, usually near the base of hummocks. S. pallustre is very common on bogs and is yellowish with distinct white patches on leaflets; similar to S. papillosum but stiffer. S. auriculatum is bright green. It is common on most bogs and forms extensive patches where it is very damp. S. cuspidatum is yellowish-green and dominates the middle of pools where the water collects because it needs the support of the water.

S. capillifolium
Bog moss with spore bodies

Sphagnum species generally hold water like a sponge, although when bound up together they can produce a very tough mat of vegetation. Within this mat large numbers of other plants can take root. These bog mosses are ion-exchanger, that is, as the water with mineral ions pass over the bog mosses the ions are absorbed into the plant and exchanged for hydrogen ions. The result is an increase in the acidity of the bog.

S. capillifolium

The leaflets have long narrow cells that enclose airspaces that hold water. Between these are the photosynthetic cells. The top of the moss is the actively growing part whilst the bottom part dies. It does not rot because of the lack of oxygen and acidic conditions, both of which inhibit the respiration of micro-organisms responsible for decomposition. Instead the dead mosses become compressed and darken with age to form peat. The continued growth each year over the peat may raise the bog with peat accumulating below. Over 1000's of years these deposits of peat may trap other organic materials, e.g. wind-blown pollen. By taking samples at different depths (ages) it is possible to deduce the type and density of the vegetation which grew at that time. This is done by analysing the preserved pollen as each species of flowering plant has a unique shaped pollen grain. The species of mosses have differing requirements for water and they form patchworks around bog pools and hummocks accordingly. In fact one can see a clear succession of species from open water through damp moss patches and then tall hummocks of moss. The latter may eventuall fall over and the cycle starts again.

Edge of a bog pool
The edge of a bog pool showing the different species of bog mosses from open water (bottom right) through to a drier heath (top left)

 


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