| Systematic problems in the neotropical moss genus Pireella range from the varietal to the generic level, involving questions of circumscription and ranking of taxonomic units at all levels, and providing an excellent focus for studies of character systems and evolutionary patterns in the Pterobryaceae and the order Isobryales. In order to circumscribe Pireella as a monophyletic unit it was necessary to study related taxa and to determine an outgroup in the family Pterobryaceae. However, relationships within the family have been little studied, and the circumscription of the family itself is questionable. A series of questions relating to the circumscription, outgroups and relationships of the order and family, and the monophyly of the genus Pireella were discussed, providing a historical background to the phylogenetic analyses. Three separate (but overlapping) analyses were used to address questions relating to the circumscription, monophyly, outgroups and relationships of the Pterobryaceae and Pireella. Characters and character states used in the phylogenetic analyses are described, and the resulting phylogenetic trees described and discussed. Very little phylogenetic structure could be discerned in the Isobryales, confirming the suspicion that the order is heterogenous (and may not be monophyletic). However, Rutenbergia and Phyllogonium were found to be closely related to the Pterobryaceae, and subsequently were used as out-groups for the family level analysis. A monophyletic group corresponding to the Pterobryaceae was found and a framework of relationships within the family was discovered. A monophyletic group corresponding to the neotropical species of Pireella was found. The paleotropical species are excluded from Pireella and probably belong in Pterobryon: however, this latter genus is badly in need of revision, and no formal transfers have been made at this point. The species accepted in Pireella are described in a monographic format, including synonymy, distribution, illustrations, maps and keys. One species of Pireella (P. fendleri) is reduced to synonymy with P. husnotiana, and the variety mexicana in P. guatemalensis is reduced to synonymy with the species. Two new species, Pireella aristata and P. laurifolia, have been described (published separately). Three major groups of species within Pirceella were found using cladistic analysis: the mariae group, the angustifolia group, and the pohlii group. |
