Macaronesia is a string of North Atlantic volcanic islands (the Azores, Madeira, Canaries, and Cape Verde) that emerged 0.4–20 million years ago and are characterized by high rates of endemism (see Juan et al. 2000 for review). Engler (1879), followed by many biogeographers (see Vanderpoorten et al. 2007 for review), proposed that Macaronesian endemics are the relics of biota that were widespread across Europe during the Tertiary and decimated on the continent during the glaciations. In contrast with the expectations of the refugium concept, however, several lines of evidence from analyses of moss species distributions (Vanderpoorten et al. 2007) and molecular evolution rates in angiosperms (Carine 2005) have recently questioned Engler's hypothesis. In mosses, the hypothesis of extinction of a Tertiary flora in all but Macaronesian areas is solely supported by extremely limited fossil evidence in the genus Echinodium (Frahm 2004). This interpretation is, however, weakened by the polyphyletic origin of the genus (Stech et al. 2008), thereby raising doubts about the actual sister relationship between fossil and extant Macaronesian Echinodium species. By contrast, the nested phylogenetic position of the Azorean endemic liverwort Leptoscyphus azoricus within a Neotropical clade (Devos and Vanderpoorten 2009); the close biogeographic affinities of several Macaronesian groups with the North and South American continents (see Vanderpoorten et al.  for review); and the polyphyletic origin among Macaronesian populations of the moss Grimmia montana, which are genetically identical or most closely related to those of different continents (Vanderpoorten et al. 2008) all point to recurrent migrations between the latter and the Macaronesian archipelagos, potentially followed by in situ speciation.
The continental extinction and recent speciation hypotheses make different predictions regarding the rates of speciation and morphological evolution. In fact, as opposed to neoendemics, which originated from local speciation processes and often underwent spectacular adaptive radiations involving a sudden burst of morphological diversification (see Gillepsie and Roderick  for review), paleoendemics, which survived continental extinctions on the islands, have most often retained a highly conserved morphology for millions, or tens of million years, to such an extent that extant taxa appear conspecific with fossil species (Sunding 1979).
In this article, we revisit hypotheses on the origin of Macaronesian endemism in the mosses from the Brachytheciaceae, subfamily Helicodontioideae. This group includes several Macaronesian endemics, namely the monotypic Madeiran Hedenasiastrum percurrens, and three Rhynchostegiella species: Rhynchostegiella bourgeana and R. trichophylla, which are restricted to the Canary Islands, and R. macilenta, whose distributions span Madeira and the Canaries. In addition, and unlike most bryophytes, a fairly well-documented fossil record is available (Miller 1984). We produced a molecular phylogeny of the Helicodontioideae to test the hypothesis of a radiation within Rhynchostegiella and date the origin of its Macaronesian endemic lineages, contrasting the results derived from a fossil calibration and an analysis employing absolute rates of molecular evolution. We then used the phylogeny to test the hypothesis of a long morphological stasis since the Tertiary period among Macaronesian endemics.