The Lichens and Lichenicolous Fungi of Belgium and Luxembourg ...

42 P. DIEDERICH & E. SÉRUSIAUX
• ecology in the study area;
• distribution in the study area; the current knowledge is given by country (Belgium,
Luxembourg, France, and occasionally Germany and the Netherlands) and within each
country by phytogeographical districts;
• useful comments;
• literature pertinent to the study area.
Taxonomy
The taxonomic concept is that accepted in modern floras, checklists or monographs. As a
rule, we do not accept species defined on chemistry alone and thus not sustained by morphological
differences, even if they can easily be recognized in the field by their distinctive
colour (e. g. strains with or without usnic acid, known in some species of Cladina,
Evernia and Haematomma).
In Cladonia, we adopt a rather strict morphological species concept, although some of
the numerous chemotaxa recognized in this genus are also distinguished by subtle morphological,
ecological or chorological characters. In such cases, we assemble all ‘taxa’
under one name, but give distribution details for all of them. For example, Cladonia
coccifera s. lat. includes C. coccifera s. s. (with zeorin), C. borealis (with barbatic acid)
and C. diversa (with zeorin); C. diversa is common in the Campinien district where the
two others are missing, whilst in the Ardenne district the three taxa occur.
Presumed species pairs, like Usnea florida and U. subfloridana, are treated as distinct
species, with the exception of Lecidella elaeochroma for which the taxonomic status of
the rather rare sorediate thalli requires further studies.
Some species belong to genera into which they have never been transferred, either
because they are poorly known (e. g. Mycoporellum sacromontanum) or due to unsolved
nomenclatural problems (e. g. Bacidina versus Woessia). Such species are cited under
the genus where they belong, but the corresponding new combination is never proposed.
Nomenclature
The nomenclature follows the International Code of Botanical Nomenclature of 1994 (the
so-called Tokyo Code).
Author abbreviations follow Kirk & Ansell (1992), except Dutch names beginning with
‘van’, like ‘van den Boom’ and ‘van Herk’, which are not abbreviated, and ‘Bouly de
Lesdain’ which is abbreviated as ‘B. de Lesd.’, and not ‘de Lesd.’. The use of ‘ex’, ‘in’ and
‘em.’ has been avoided, making the author citations as short as possible (e. g. Lecanora
conizaeoides Cromb., instead of ‘Nyl. ex Cromb.’; Lecania inundata (Körb.) M. Mayrhofer,
instead of ‘(Körb.) M. Mayrhofer in Nimis & Poelt’; Lecanora gisleriana Müll. Arg.,
instead of ‘Müll. Arg. em. J. Steiner’).
Nomina nuda and ‘ad int.’ names, i. e. not validly published names, are avoided as much
as possible, unless they have already been published elsewhere, or if they are in press