Environmental variation obscures species diversity in southern European populations of the moss genus Ceratodon

Abstract

A major problem in taxonomy is to determine if morphological variation in field collected specimens is caused by genetic differentiation, and therefore corresponds to evolutionary distinct units, or is caused by environmental variation acting on a single interbreeding population. We made a biometric study in the moss genus Ceratodon, based on plants sampled from mountainous areas of the Mediterranean region, and other mountain regions and lowlands, mostly from southern Europe. To determine whether morphological variation in field collected plants is constant growing in laboratory conditions, we generated in vitro cultures. A total of 22 morphological characters were measured and analyzed statistically, for which we considered the results obtained from parallel phylogenetic and genome size studies published previously. In spite of the changes induced by environmental conditions, we found clear biometric discontinuity between some plants collected from southern Spain, and those from other parts of the world. This discontinuity is supported by flow cytometry, as well as by genetic data. In contrast, a group of samples considered of hybrid origin do not show morphological differences with respect to those from southern Spanish mountains with differentiated genotype and genome size. Integrative taxonomy based on genetic, genome size and morphological data unambiguously support the recognition of a new species, Ceratodon amazonum. Moreover they suggest that the previously recognized C. conicus is a recombinant between C. purpureus and C. amazonum and is considered here to be a nothospecies, for which an epitype is here designated because the lectotype is demonstrably ambiguous.