| This monograph brings together all previous information about the fern genus Polybotrya (Dryopteridaceae) and includes many new observations based on my studies of over 2500 herbarium sheets from 29 herbaria and on seven months of field work in tropical America. Polybotrya is subdivided into three easily identified subgenera--Soromanes, Sorbifolia, and Polybotrya--and consists of 35 species, ten of which are new. The center of diversity for the genus is the Andes, where there are 23 species, 12 of which are endemic. The coastal mountains of southeastern Brazil are notable because they contain five species, all endemic. Morphologically, Polybotrya is unusual because of its high-climbing stem and strongly differentiated sterile and fertile leaves. Furthermore, the stem contains a unique dictyostele. Three types of sori occur in the genus: botryoid, coenosoric, and a new type here termed "amphiacrostichoid." Two hypotheses are offered that explain the evolution of these three types of sori. Coenosoric and amphiacrostichoid sori contain diplodesmic veins, which I found to be developmentally homologous with veins of the sterile leaf. In Polybotrya, sterile-fertile leaf differentiation illustrates how dimorphy entails many characters, not merely a reduction of the laminar tissue. Evolutionarily, Polybotrya is probably derived from a Cyclodium-like ancestor. Maxonia, a genus that looks like Polybotrya, is probably derived from Arachniodes and is not ancestral to Polybotrya as pteridologists had previously thought. My treatment of Polybotrya differs from those of other recent pteridologists because P. cervina is placed in the monotypic genus Olfersia.; Each species treatment includes complete synonymy, description, discussion, and list of specimens examined. In addition, each species has a full-page illustration showing characters useful in identification and a distribution map. Also listed are the names of uncertain application and excluded taxa. Finally, indices to collector's numbers and taxonomic names are provided. |
