Is the hairy vaginula an diagnostic feature in the taxonomy of the genus Orthotrichum?

The location of stomata and the structural details of exostome teeth and endostome segments are among the most important taxonomic features used for identifying Orthotrichum species. Certain species pairs (e.g. O. stramineum vs. O. pallens; O. pumilum vs. O. stellatum) are distinguished based on the presence or absence of hair on the vaginula. The authors have shown that this feature is not always appropriate for species identification. Some specimens of O. affine, O. anomalum or O. speciosum were found to have a hairy vaginula, although this feature is not included in their description. The confusion with species determination was resolved in a subsequent DNA analysis of the specimens. The reliability of this character is briefly discussed in the paper.