A PHENETIC AND PHYLOGENETIC ANALYSIS OF THE HYLOCOMIACEAE AND RHYTIDIACEAE

Abstract

  Unclear relationships among the genera of the Hylocomiaceae and Rhytidiaceae, as presented by Brotherus in Die natürlichen Pflanzenfamilien, have resulted in a variety of taxonomic treatments. Whereas Fleischer emphasized growth pattern when he created the families, later workers have put greater emphasis on paraphyllia and peristome structure.

  Similarity graph clustering was used to estimate phenetic relationships on the basis of 50 morphological characters describing 71 species that represent the study group and several related families. Loeskeobryum is more similar to Rhytidiadelphus than to Hylocomium or Hylocomiastrum. These four genera plus Neodolichomitra form a reasonably distinct cluster. Pleurozium, Rhytidiopsis, and Rhytidium are phenetically isolated, yet they show some similarity to this cluster. Cryptoneurum, Okamuraea, Ptychodium, and Rigodiadelphus [“Lesquereuxia”] show very little similarity to other genera of the study group.

  Phylogenetic relationships among the genera were explored using character compatibility and parsimony analyses. The most parsimonious phylogenetic hypotheses and the one supported by the most credible clique of compatible characters place many genera from the study group on a clade defined by a weft life form. Hypotheses of evolutionary relationship based on growth pattern, paraphyllia, and peristome structure are incompatible. Hypotheses based on growth pattern and paraphyllia suggest that Hylocomiastrum, Hylocomium, and Loeskeobryum form a monophyletic group, whereas hypotheses based on exostome ornamentation and perforation of endostome segments suggest that Hylocomium and Pleurozium form a monophyletic group that is part of a larger clade composed of these two genera plus Loeskeobryum and Rhytidiadelphus.

  The Hylocomiaceae are redefined as a monophyletic family of cool-temperate to subarctic, weftforming mosses. Twelve genera are included in the family: Hylocomiastrum, Hylocomium, Leptocladiella, Leptohymenium, Loeskeobryum, Macrothamnium, Neodolichomitra, Orontobryum, Pleurozium, Rhytidiadelphus, Rhytidiopsis, and Rhytidium. Rhytidiaceae is synonymous with Hylocomiaceae. The following genera, which at one time or another have been included in the Hylocomiaceae or Rhytidiaceae, are excluded from the family and assigned elsewhere: Cryptoneurum (Brachytheciaceae), Cyathothecium (Hypnaceae), Gollania (Hypnaceae), Macrothamniella (Hypnaceae), Okamuraea (Leucodontaceae), Ptychodium (Thuidiaceae), Rigodiadelphus (Leskeaceae), and Stenotheciopsis (Hypnaceae).