A British Red Data Book for bryophytes is in preparation by the British Joint Nature Conservation Committee (see British RDB species recorded in Wales) and a European Red Data Book for Bryophytes has recently been published (see European RDB species recorded in Wales).

In addition, as a result of the Biodiversity Convention signed up to by Britain at the Earth Summit in Rio de Janeiro in 1992 the UK government has drawn up a list of "key species" (including bryophytes) present in Britain which are threatened globally. Action Plans have been prepared for some of these species, and are due to be drawn up for others. (See Key biodiversity species recorded in Wales).

In recent Red Data Books the species included are categorised according to criteria drawn up by the World Conservation Organisation (IUCN). These criteria have been modified for the European Bryophyte Red Data Book to make them more applicable:

EXTINCT (Ex)

"Taxa for which all known localities have been checked in the last 30 years without success, or taxa listed as extinct or vanished in all available Red Lists, if the area of distribution is covered by Red Lists." The category Ex is used only when a species is thought no longer to exist anywhere in the World.

VANISHED (Ev)

"Taxa considere extinct in a country, or in Europe, but still extant elsewhere in the world." The category Ev is used to distinguish these taxa from those that are truly extinct in the World.

ENDANGERED (E)

"Taxa in danger of extinction or vanishing and whose survival is unlikely if the causal factors continue operating, or taxa considered endangered in most of the European Red Lists, or taxa for which a considerable number of their known localities have been checked without success in the last 30 years."

VULNERABLE

"Taxa believed likely to move into the ENDANGERED category in the near future if the causal factors continue operating." For European bryophytes the following guidelines were used in assigning species to this category:

• all species occurring in very few localities should be at least Vulnerable, if not Endangered, unless there is good reason for excluding them from either of these categories;
• species listed as Vulnerable in all but one available Red Lists should be considered;
• species that have declined over a considerable part, or preferably throughout, their range should be considered.

It is suggested that the species in this category should be critically re-examined after further survey and monitoring.

RARE (R)

"Taxa occurring in fewer than 40 of the 50x50km squares in Europe or fewer than 5% of the squares in their main areas of distribution."

INSUFFICIENTLY KNOWN (K)

"Taxa known to be very restricted in distribution, but for which more survey work is required before they can be placed with certainty in one of the preceding categories."

TAXONOMICALLY ILL-DEFINED (T)

"Taxa with obvious taxonomical problems or of doubtful value, and therefore impossible to consider objectively in a Red List".

REGIONALLY THREATENED (RT)

"Taxa not obviously threatened in the whole of Europe but threatened in or vanished from a large part of it".

NOT THREATENED (NT)

"Taxa obviously not threatened now, even when showing some signs of regression."