The acrocarpous moss genus Timmiella is a poorly understood group of nearly cosmopolitan distribution. Found in Mediterranean climates on every continent but Antarctica, this drought-tolerant genus has uncertain phylogenetic position and uncertain species diversity. Timmiella is represented by two recognized species on the west coast of North America and at least two in the Mediterranean, and so serves as a good candidate for exploring the Madrean-Tethyan hypothesis. The taxonomic status, historical relatedness and biogeography of these two species are addressed in the present study. Using neutral molecular markers from the nuclear (ITS-2) and chloroplast (atpB-rbcL spacer) compartments, we estimate phylogenetic relationships between extant populations. We measure genetic diversity within populations, but cannot estimate population genetic parameters using the coalescent owing to the inapplicability of a molecular clock. We detect well-supported phylogenetic incongruence between chloroplast and nuclear data sets. Most likely phylogenetic reconstructions among Californian samples show geographical discordance suggesting that the two west coast species are polyphyletic or of dubious species status. One long-distance dispersal event between California and Egypt is detected. T. barbuloides, endemic to the Mediterranean, is also polyphyletic in some analyses.

Key words: Madrean-Tethyan, phylogeography, species concept, Timmiella