Pantropical epiphytic rain forest bryophyte communities - coeno-syntaxonomy and floristic-historical implications
Kürschner, Harald; Parolly, Gerald
The trunk-epiphytic bryophyte vegetation of tropical lowland and mountain rain forests (Africa, Southeast Asia, South and Central America) is reclassified coeno-syntaxonomically under the focus of symphylogenetic, evolutionary, and palaeohistorical implications. This is the first tropic-wide approach to combine the oligophotic bryophyte communities in units based on supraspecific taxa. The grouping finally achieved deviates considerably from the results obtained by previous phytosociological studies where 11 alliances, six orders, three classes, and one class group were recognized. The coeno-classification distinguishes only two major groups within a common Coeno-Plagiochiletea class: The Coeno-Ptychanthetalia of the lowland and submontane tropics and the montane Coeno-Bazzanio-Herbertetalia. Thus, the low-altitudinal communities - and the high-altitudinal communities respectively - resemble each other more pantropically than the lowland and montane bryophyte vegetation units within one continent. The coeno-communities are united transgressively by many bicontinentally or pantropically distributed coeno-taxa especially at section-level, comprising vicarious and pseudovicarious species. The Coeno-Plagiochiletea can be fully equated with the highest syntaxonomic unit, the Lejeuneo flavae-Frullanea ericoidis class group. Owing to the great number of vicariants and pseudovicariants composing the different communities transcontinentally, the Lejeuneo flavae-Frullanea ericoidis consist of geosynvicariants at class-, order-, and alliance-level with a joint evolution. These relationships are discussed with respect to palaeogeographic events. Especially Afro-American disjunctions at the level of close relatives are recorded, but few indications support the concept of a common Palaeotropis. In taxa of the shaded understory of primary rain forests, with the prevailing "passive" or "vegetative" life history strategies, these links (and also the pantropical distributional pattern) may date back to before the South Atlantic had fully opened in mid-Cretaceous. Thus, parallel differentiations have taken place in the different parts of the tropical biome (continents), modifying the joint mid-Cretaceous floristic stock in coevolutional processes under comparable conditions. Both the ecological and the historical background is highlighted by presenting examples of parallel evolution (e.g., Lejeuneaceae: Ptychanthinae, Geocalycaceae: Leptoscyphus-Heteroscyphus complex) within trunk epiphytes in detail. The symphylogenetic considerations effectively substitute and support the syntaxonomic classification. Additionally, the category "class group" is redefined coeno-syntaxonomically to classify major vegetation units (often of different continents) with parallel evolutional trends of a common floristic stock.