With something as complex and variable as vegetation, no key can pretend to offer an infallible short cut to diagnosis. The following should thus be seen as simply a crude guide to identifying the types of mire vegetation in the scheme and must always be used in conjunction with the data tables and community descriptions. It relies on floristic (and, to a lesser extent, physiognomic) features of the vegetation and demands a knowledge of the British vascular flora and, in many cases here, of bryophytes. It does not make primary use of any habitat features, though these may provide a valuable confirmation of a diagnosis.

Because the major distinctions between the vegetation types in the classification are based on inter-stand frequency, the key works best when sufficient samples of similar composition are available to construct a constancy table. It is the frequency values in this (and, in some cases, the ranges of abundance) which are then subject to interrogation with the key. Most of the questions are dichotomous and notes are provided at particularly awkward choices or where confusing zonations are likely to be found.

Samples should always be taken from homogeneous stands and be 2 × 2m or 4 × 4m according to the scale of the vegetation or, where complex mosaics occur, of identical size but irregular shape. Very small springs or flushes can be sampled in their entirety.

1 At least some Sphagna constant and often forming an important structural element in the vegetation 2

Sphagna at most occasional and patchily prominent and often altogether absent 34

2 Sphagnum auriculatum constant and locally abun dant in spring-head, soakway or pool vegetation with some of Hypericum elodes, Potamogeton polygonifolius, Juncus bulbosus, Ranunculus flammula, Deschampsia cespitosa, Saxifraga stellaris, Ranunculus omiophyllus, Montia fontana, Anthelia julacea, Philonotis fontana, Scapania undulata, Marsupella emarginata, Dicranella palustris 14

Sphagnum auriculatum can be frequent but not with the above 3

3 Sphagna occurring as an extensive carpet or in patches with graminoid monocotyledons (some of Scirpus cespitosus, Eriophorum vaginatum, E. angustifolium, Molinia caerulea) and sub-shrubs (some of Erica tetralix, Calluna vulgaris, Myrica gale, Vaccinium spp., Empetrum sspp.) 17