Synonymy

Koenigia islandica-Carex demissa nodum Birks 1973.

Constant species

Carex demissa, Deschampsia cespitosa, Juncus triglumis, Koenigia islandica, Saxifraga stellaris, Blindia acuta, Scapania undulata.

Rare species

Juncus biglumis, Koenigia islandica, Sedum villosum.

Physiognomy

Since it was first found in Britain in 1934 and finally accurately determined in 1950 (Burtt 1950, Raven & Walters 1956), Koenigia islandica has been observed on and around The Storr in Skye, where it was first collected, on other parts of the Trotternish ridge there (Birks 1973) and on Mull (Birse 1984), in a variety of vegetation types. In certain cases it is best seen as an occasional, sometimes of quite high local cover, in communities which occur widely elsewhere: some stands, for example, can be placed in the Philonoto-Saxifragetum, while others are very similar to the Festuca-Agrostis-Alchemilla or Carex-Poly trichum grassheaths. Others, however, are more peculiar and it is these which are gathered into this Carex demissa-Koenigia islandica community.

It is an open vegetation type, with a bryophytedominated carpet broken by areas of wet, silty and stony ground. Scapania undulata, Calliergon sarmentosum and Blindia acuta are all common and each can be abundant, with occasional patches of Dicranella palustris, Philonotis fontana, Drepanocladus revolvens, Marsupella aquatica and Sphagnum auriculatum. Scattered through this mat and over the rills themselves are plants of Carex demissa, Koenigia, Deschampsia cespitosa, Saxifraga stellaris, Juncus triglumis, J. bulbosus and the rare J. biglumis and Sagina saginoides. All of these are generally of low cover, though many can show a measure of abundance and Koenigia itself, though its individual plants are little more than a few centimetres across, can cover quite an area of ground.

Habitat

In common with many of the other situations in which Koenigia is found, both in this country and elsewhere, the Carex-Koenigia community occurs on ground which is kept periodically moist by circumneutral and oligotrophic waters. Typically, it is found in open silty or stony flushes fed by vigorous seepage from spings issuing at moderately high altitudes, over 500 m, from the basalt of the Trotternish ridge.