Epiphytism and generic endemism in the Hypnodendrales: Cyrtopodendron, Franciella and macro–morphological plasticity

Abstract

The Hypnodendrales are an order of generally very robust pleurocarpous mosses in which most taxa have one of three distinct growth forms. The group includes four monotypic genera, two of which, Cyrtopodendron and Franciella, are endemic to New Caledonia. We investigate the phylogenetic relationships of these two taxa and of Pterobryella rigida, also a New Caledonian endemic, and demonstrate that Cyrtopodendron and Franciella should be recognised within Pterobryella and Spiridens respectively as P. vieillardii and S. spiridentoides. We further use Bayesian methods to reconstruct ancestral character states for macro–morphological type and substrate preference within the order, to evaluate hypotheses of correlated evolution of these morphological and ecological characters, and to test for directionality in their evolution. The results suggest that macro–morphology evolves in conjunction with shifts between epiphytic and non–epiphytic substrates, with the dendroid architecture strongly associated with non–epiphytic substrates and the morphologies we term “stipitate–frondose” and “spiri–dentoid” associated with epiphytism. Ancestral character state reconstruction challenges previous hypotheses that the strictly dendroid form is plesiomorphic within the Hypnodendrales and suggests that the stipitate–frondose architecture may have arisen very early within the evolution of the group, although states for the earliest nodes remain ambiguous. The spiridentoid growth form characteristic of Spiridens, Cyrtopus and Bescherellia may be inherited from a shared common ancestor, with the dendroid morphology of Hypnodendron s.str. being derived, while within Pterobryella the balance of evidence favours an epiphytic, stipitate–frondose common ancestor from which the lithophytic species found on New Caledonia and Lord Howe are descended. Transitions between the major growth forms found within the order are highly homoplastic, facilitating adaptive shifts between epiphytic and non–epiphytic substrates and explaining the paraphyly of some previously recognised genera and families.The Hypnodendrales are an order of generally very robust pleurocarpous mosses in which most taxa have one of three distinct growth forms. The group includes four monotypic genera, two of which, Cyrtopodendron and Franciella, are endemic to New Caledonia. We investigate the phylogenetic relationships of these two taxa and of Pterobryella rigida, also a New Caledonian endemic, and demonstrate that Cyrtopodendron and Franciella should be recognised within Pterobryella and Spiridens respectively as P. vieillardii and S. spiridentoides. We further use Bayesian methods to reconstruct ancestral character states for macro–morphological type and substrate preference within the order, to evaluate hypotheses of correlated evolution of these morphological and ecological characters, and to test for directionality in their evolution. The results suggest that macro–morphology evolves in conjunction with shifts between epiphytic and non–epiphytic substrates, with the...

Lobule shape evolution inRadula(Jungermanniopsida): one rate fits all?

“…ex Mitt. expressing morphologies equivalent to Niklas' () simulated models grow on horizontal surfaces (Bell et al ., ). Tree trunks present vertical surfaces in the low‐light and generally high‐humidity forest interior environment that permit morphologies maximizing light interception to occur above ground level.…”

“…Some taxa of Hypnodendrales, such as Braithwaitea Lindb. and Dendro‐hypnum Hampe, have shifted to growth on vertical surfaces (Bell et al ., ), where the planar space‐filling shoot system in these species receives structural support from a lateral attachment point provided by a large robust primary stem possessing a heavily secondarily thickened cortex. If the optimization of light interception is a prerequisite of form permitting growth on lower tree trunks, we might expect the evolution or maintenance of planar space‐filling shoot systems supported laterally by a robust axis in lineages that transition to inhabitation of tree trunks.…”

“…However, evidence for morphological plasticity and, perhaps, even rapid morphological evolution has been found in both mosses and liverworts (e.g. Vanderpoorten et al ., ; Bell, Newton & Hyvönen, ; Yu et al ., ), with the exception of Devos & Vanderpoorten (), studies have not estimated time‐calibrated rates of change.…”

Multiple innovations underpinned branching form diversification in mosses

“…Fig. m) are strongly associated with terrestrial substrates (Bell et al ., ). Together, the data suggest that both developmental innovations and environmental drivers contributed to branching form diversification in mosses, and that mosses and vascular plants are likely to have diversified in response to distinct selective pressures.…”

Three modes of heterochrony explain lobule diversity inRadulasubgenusCladoradula(Porellales: Jungermanniopsida), a small lineage of early land plants today

“…A plane‐filling morphology was found to optimize light interception (Niklas, ), and this form is expressed by species of Hypnodendrales (i.e. Bell, Newton & Hyvönen, ) that grow in terrestrial microsites from horizontal surfaces. Large space‐filling bryophytes are expected to outcompete small compact forms for space and light (Proctor, ), by spreading photosynthetic tissue more diffusely in space (Monsi, Uchijima & Oikawa, ).…”