A developmental, phylogenetic and taxonomic study on the moss genus Taxithelium Mitt. (Pylaisiadelphaceae)

Mosses are the second largest group of land plants. Hypnales, an order of pleurocarpous mosses, include ca. 50% of all mosses. The family Sematophyllaceae is probably the most diverse Hypnales in the tropics and one of the most complex and taxonomically confused. Traditionally variation in characters of the sporophyte have been used to distinguish genera and even species, but in this study characters of the gametophyte have been found to provide valuable distinctions. This thesis comprises three parts: (1) a micromorphological study of papilla development in Taxithelium and relatives; (2) a phylogenetic study of Taxithelium; and (3) a revision of Taxithelium subgenus Vernieri.;1. Micro-morphological studies on mosses are not common, but can illuminate the nature of taxonomic characters. I present data on the structure and development of leaf cell papillae in different Sematophyllaceae to assess their developmental similarity and also the congruence between papilla morphology and taxonomy. Two kinds of papillae are recognized. One is dome-shaped to conical tapering to a firmly rounded apex ("conical"), whereas the other presents a more flaccid, baggy appearance, and is often flat-topped and wider at the apex than at the base ("baggy"). The two types of papillae are also developmentally distinct: Conical papillae first appear as slight protrusions that gradually increase in height, whereas baggy papillae change shape as they develop. Conical papillae occur in most papillose taxa, whereas baggy papillae are present only on Taxithelium subgenus Taxithelium.;2. In order to test infrageneric classifications and species delimitation within Taxithelium, I constructed a molecular phylogeny using three chloroplast DNA loci (trnL, psbT and rps4), three mitochondrial DNA loci ( rps3, nad5 and nad4--5) and a nuclear gene (ho1). Analyses of the loci separately and in various combinations all support the monophyly of Taxithelium, which is probably of SE Asian origin. Two major clades corresponding to subgenera (see below) were resolved within the genus. The first clade is composed of at least four smaller clades, three of which include only SE Asian plants and one is from the Americas; the latter is nested within the SE Asian clades. The second clade appears to have a Southeast Asia origin and shows two dispersal events to America. Data show that T. merrillii, T. concavum, T. pluripunctatum, T. planissimum and T. isocladum are each demonstrably monophyletic units. On the other hand, T. planum, T. nepalense and T. instratum as circumscribed today are polyphyletic. Taxithelium lindbergii can be considered monophyletic only with the inclusion of T. alare. The ho1 nuclear locus is used for the first time in bryological studies, and with promising results.;3. Taxithelium is highly variable morphologically and includes plants with pluripapillose leaf cells as well as plants that lack papillae. Based on the results above Taxithelium is newly re-circumscribed and includes two subgenera, Taxithelium and Vernieri, that differ in papilla morphology. Detailed morphometric studies were carried out in subgenus Vernieri, individual analyses including different subsets of provisionally recognized groups. Based on these studies, eleven species could be recognized, one from Africa, two from the Americas, and the rest from Southeast Asia and Pacific Islands. A key to identify all the species recognized is provided, as well as full descriptions, nomenclature, distribution maps, etc., of each species. One species, T. damanhurianum, is new to science and is described from Seram, Indonesia.