Brachytheciaceae clade

FIGURE 6.2 The Brachytheciaceae clade from the single most parsimonious tree based on direct optimization analyses of molecular (cp psUY-R and tmh-P, and nr ITS2) and morphological data (based on Huttunen et ah, 2004). 

Once the main clades within the Brachytheciaceae had become more or less stabilized, our main goal was to elucidate the position of taxa not included or not well represented in the previous analyses, and also to find additional arguments for generic and subfamilial placement of some particular taxa. Three methods are involved here (1) evaluation of the molecular synapomorphies in POY alignment, i.e., characteristic indel events and substitutions (2) analysis of the secondary structure of the tmL intron and (3) phylogenetic analysis of a reduced dataset from previous analyses, with some additional taxa. 

The genera of Brachytheciaceae are quite diverse with respect to the level of substitution/indel events within the tmL intron (Appendices 6.1 and 6.2). Very few (0 to 3) substitution/indel events are observed in all members of the Homalothecioideae, most members of the Brachythecioideae (with the exception of Sciuro-hypmm and four species closely related to Brachythecium salebrosum, which have a long insertion), as well as basal groups of the Helicodontioideae (Squamidium clade),... 

It remains unclear if there are any environmental factors responsible for such a high level of substitutions in the Oxyrrhynchium-Donrichardsia clade and in the Sciuro-hypnum clade. The only correlation we could notice is that both groups are quite rich in eutrophic species, common on humus and decaying wood, which is somewhat less characteristic for other genera of Brachytheciaceae. 

The nodes subtending the three major taxa (Dicranidae node 50, paraphyletic Bryanae nodes 58 to 66, Hypnanae node 86) are dated within the Jurassic. However, much of the species diversity in these clades has arisen much more recently, during the Cretaceous or Cenozoic (Figure 17.1). The Pottiaceae (here with a distal node dated within the Cenozoic) are well known as a highly diverse but taxonomically difficult lineage (Zander, 1993) and at least the three most diverse of the pleurocarp families (Brachytheciaceae, Hypnaceae and Sematophyllaceae) are also problematic. 

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