Morphological homoplasy is reputed to be prevalent in plants, perhaps especially in mosses and other haploid-dominant ‘bryophytes’. The Calymperaceae is a diverse and ecologically important family of mosses in the tropics that has proven difficult to place phylogenetically and circumscribe taxonomically; single characters are not often definitive and supra-specific taxa are mostly defined by tenuous combinations of morphological features. Using morphological characters, as well as sequence data from the plastid-encoded genes rbcL and rps4, we reconstructed a phylogenetic framework in which to explore character evolution in the Calymperaceae and putative relatives, particularly, the origin and evolution of a distinctive leaf anatomy seen most prominently in Leucobryum and similar taxa. This generalized ‘leucobryoid’ leaf type contains living green cells that are covered with empty dead hyaline cells. We showed that a monophyletic Calymperaceae can only be defined by including several leucobryoid genera within the traditional family; in fact, our topologies confirm that the leucobryoid leaf architecture evolved independently at least four times within our taxon sample. The phylogenetic patterns probably denote both convergence and parallelism. When mapped to the phylogenies (using several different quantitative comparative methods), coarse habitat characterizations of sampled leucobryoid taxa appear to falsify previous adaptive hypotheses and yet provide no obvious clues about why this leaf architecture might be favored. If one considers all the various extant moss taxa with hyalocyst-dominated architectures then there might conceivably be one common denominator: their respective oligotrophic habitats.

Key words: Calymperaceae, convergence, homoplasy, leaf architecture, oligotrophy, parallelism