Morphology informed by phylogeny reveals unexpected patterns of species differentiation in the aquatic moss Rhynchostegium riparioides s.l.

Abstract

a b s t r a c tBryophyte floras typically exhibit extremely low levels of endemism. The interpretation, that this might reflect taxonomic shortcomings, is tested here for the Macaronesian flora, using the moss species complex of Rhynchostegium riparioides as a model. The deep polyphyly of R. riparioides across its distribution range reveals active differentiation that better corresponds to geographic than morphological differences. Morphometric analyses are, in fact, blurred by a size gradient that accounts for 80% of the variation observed among gametophytic traits. The lack of endemic diversification observed in R. riparioides in Macaronesia weakens the idea that the low rates of endemism observed in the Macaronesian bryophyte flora might solely be explained by taxonomic shortcomings. To the reverse, the striking polyphyly of North American and European lineages of R. riparioides suggests that the similarity between the floras of these continents has been over-emphasized. Discriminant analyses point to the existence of morphological discontinuities among the lineages resolved by the molecular phylogeny. The global rate of error associated to species identification based on morphology (0.23) indicates, however, that intergradation of shape and size characters among species in the group challenges their identification.

Empirical Evidence Supporting Frequent Cryptic Speciation in Epiphyllous Liverworts: A Case Study of the Cololejeunea lanciloba Complex

“…Despite our limited understanding of the processes, some evidence indicates that the origin of some or many cryptic species may coincide with the adaptation to extreme habitats [1,2]. This hypothesis is consistent with the observation of large number of cryptic species of animals occurring in extreme habitats [3-5] and cryptic land plant species growing either in aquatic or epiphyllous habitats [6-9] or in habitats with considerable desiccation stress [10]. However, this hypothesis may be correct for some but very unlikely for all cases of cryptic species diversity as indicated by cryptic species of animal and plant lineages that don’t occur in extreme habitats [11-14].…”

“…Natural selection was considered to foster cryptic species via direct and/or indirect selection on phenotype and/or reproductive traits [6,53,54]. In our case, epiphyllous liverworts likely experience strong selection on morphological characters that are critical for the survival of these plants in harsh condition-at the surface of living leaves.…”

Molecular Phylogeny of the Leafy Liverwort Lejeunea (Porellales): Evidence for a Neotropical Origin, Uneven Distribution of Sexual Systems and Insufficient Taxonomy

“…After three centuries of morphology-based research a plethora of taxa have been proposed in this genus, of which only a small part has been included in modern revisions, reflecting the limited number of liverwort specialists dealing with these taxonomically difficult plants. Our molecular data add to growing evidence that not all biologically relevant entities can be detected using solely morphology, and that the acceptance of a considerable intraspecific morphological variation may lead to an underestimation of the actual number of biological species [109], [110]. Thus, concepts considering cryptic and semi-cryptic species may provide more realistic estimates than the current practice.…”

New insights into the phylogeny and relationships within the worldwide genus Riccardia (Aneuraceae, Marchantiophytina)

“…The latter case may be verified with tools such as Haplowebs (Fontaneto et al 2015). Non-monophyly of species is frequently detected in bryophytes and molecular analyses are an important tool to reveal the existence of morphologically distinct species that would otherwise have remained undetected (e.g., Sukkharak et al 2011;Hutsemékers et al 2012;Aranda et al 2014;Hedenäs et al 2014;Heinrichs et al 2015).…”