Organisation of the checklist - 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 Cladonia, 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.
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.