|dc.description.abstracteng||Lejeuneaceae represent the most species-rich epiphytic lineage of leafy liverworts with approximately 1000 species in 68 currently accepted genera. This subcosmopolitan family has its centre of diversity in the humid tropics and constitutes an important component of cryptogamic, especially epiphytic diversity. Lejeuneaceae are characterized by incubous leaves divided into a large dorsal lobe and a small ventral, usually 1-3 toothed lobule which is broadly attached to the lobe along a keel, a hyaline papilla situated near the lobule apex, beaked perianths within each one archegonium, and the occasional occurrence of ocelli. Morphological and molecular studies resolved the family in two subfamilies and four main lineages. However, the systematic position of many taxa and their delimitations are still subject to controversy. To clarify these issues, my study focused on several critical genera using three molecular markers (cp rbcL and trnL-F, nrITS) and a dense taxonomic sampling. Phylogenetic analyses resolved the relationships within Diplasiolejeunea and Lejeunea, and clarified the systematic positions of Microlejeunea, Harpalejeunea, Myriocolea, Sphaerolejeunea, and Bromeliophila.
A molecular phylogenetic study of Diplasiolejeunea points to extensive morphological homoplasy but allows to assign three main clades to subgenera. The phylogeny supports a deep split into a Neotropical and a Paleotropical clade, the latter structured into Australasian, Asian and Afromadagascan lineages. The Neotropical clade is further subdivided into two geographically and ecologically separated lineages, the epiphytic montane subgenus Physolejeunea and the epiphyllous lowland subgenus Diplasiolejeunea. This strong correlation between ecological traits and geographical distribution range could indicate the rise of the Andes’ influence in stimulating the diversification of Physolejeunea, perhaps by providing new habitats. A few Diplasiolejeunea species have intercontinental ranges. Range formation of Cenozoic Diplasiolejeunea is obviously a result of rare long distance dispersal, frequent short distance dispersal, extinction, recolonization, and niche conservatism.
Lejeunea is one of the largest genera of Lejeuneaceae. My molecular studies resolved Lejeunea in two robust lineages, corresponding to L. subg. Lejeunea and L. subg. Crossotolejeunea. Neotropical accessions dominate early diverging lineages of both main clades of Lejeunea. This pattern suggests an origin in the Neotropics followed by several colonizations from the Neotropics into the Paleotropics and vice versa. Most Afromadagascan clades are related to Asian clades. Several temperate Lejeunea radiations were detected. 82 of the 91 investigated Lejeunea species could be identified to species level. 54 species were represented by multiple accessions, of these, 25 para- or polyphyletic, 29 monophyletic. L. subg. Lejeunea shows a tendency of monoecy whereas L. subg. Crossotolejeunea shows a tendency of dioecy. Some dioecious as well as some monoecious species have disjunct ranges. Using molecular and morphological evidence, Harpalejeunea fischeri, H. filicuspis, H. latitans and Pluvianthus squarrosus were transferred to Microlejeunea. Two monotypic genera, rheophytic Myriocolea and epiphyllous Sphaerolejeunea were transferred to Colura and Lejeunea respectively. Our studies also confirmed the monophyly of Bromeliophila and provided evidence for a sister relationship of Bromeliophila and Prionolejeunea; this clade is in turn sister to Cyclolejeunea. Despite an extensive morphological overlap, Bromeliophila is not closely related to Lejeunea.||de