498 TAXON 61 (3) • June 2012: 498–514 Bell & al. • Epiphytism in the Hypnodendrales INTRODUCTION The historical diversification of the pleurocarpous mosses has frequently been linked directly or indirectly to epiphytism. While the pleurocarpous condition as a potential key innova- tion clearly facilitates a greater variety of plant architectures (e.g., Bell & Newton, 2007; Newton, 2007), many of which are exploited by epiphytes, it has further been suggested that an expansion of epiphytic niches associated with the development of angiosperm forest ecosystems in the late Mesozoic may have initiated a pleurocarpous evolutionary radiation (Buck, 1991; Kürschner & Parolly, 1999; Shaw & al., 2003). Although hypothesised timelines for the diversification of pleurocarps and the origins of complex angiosperm forests cast some doubt on this (Newton & al., 2007), clearly a significant percentage of extant pleurocarps are strongly adapted to lifestyles as fac- ultative or obligate epiphytes, a factor that must to some extent underlie their unique diversity. Much research has focused on the phylogenetic mutabil- ity of morphological character suites associated with epiphyt- ism in the homocostate pleurocarps (i.e., the Ptychomniales, Hookeriales and Hypnales; Bell & al., 2007b) and their poten- tial to mislead systematics (e.g., Hedenäs, 1997, 2001, 2002; Buck & al., 2000; Vanderpoorten & al., 2002; Huttunen & al., 2004; Olsson & al., 2009). The Hypnales in particular are an actively evolving and relatively recently radiated group, and as such are characterised by short branches and a paucity of synapomorphies hindering phylogeny reconstruction (Huttunen & al., in press). The widespread correlated evolution of char - acters associated with epiphytism further complicates matters. However, the link between the pleurocarpous condition and the propensity for repeated parallel evolution (and re-evolution) of epiphytism and putatively associated character traits extends back to the origin of the pleurocarps, albeit often expressed through different bauplans (Bell & Newton, 2007). These earlier diverging pleurocarpous and partially pleurocarpous lineages, Epiphytism and generic endemism in the Hypnodendrales: Cyrtopodendron, Franciella and macro-morphological plasticity Neil E. Bell, 1,3 Angela E. Newton2 & Jaakko Hyvönen3 1 Botanical Museum, P.O. Box 7, 00014 University of Helsinki, Finland 2 1 Cayzer Court, Gartmore, Stirling, FK8 3RE, U.K. 3 Department of Biosciences (Plant Biology, Biocenter 3), P.O. Box 65, 00014, University of Helsinki, Finland Author for correspondence: Neil E. Bell, neil.bell@helsinki.fi 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 adap- tive shifts between epiphytic and non-epiphytic substrates and explaining the paraphyly of some previously recognised genera and families. Keywords ancestral character state reconstruction; moss phylogeny; New Caledonia; pleurocarpous mosses; Pterobryella; Spiridens Supplementary Material The alignment file is available in the Supplementary Data section of the online version of this article (http://www.ingentaconnect.com/content/iapt/tax). SYSTEMATICS AND PHYLOGENY