Grout (1936) lectotypified Dicranella with a species of Anisothecium, but this choice can be rejected since it was a mechanical selection using Canon 15 of the International Code of Botanical Nomenclature (Greuter et al. 1988).
Microdus differs from Dicranella in having reduced, irregularly papillose peristome teeth and warty spores. Most peristomes in Dicranella are well-developed and have papillae arranged in distinct rows, but some species have reduced, weakly striate-papillose peristome teeth. There is a complete series of intermediates between the typical Microdus and Dicranella peristomes, both genera have species with warty spores. Microdus is treated as a synonym of Dicranella here.
Dicranella is a member of a generic complex whose internal boundaries are based solely on sporophytic features. Generic relationships are blurred by the reticulate distribution of sporophytic character states (see Table 1). Character expression is variable in the group, i.e., consistently expressed in one genus but variable in another.
Table 1. Distinguishing features of the Dicranella-complex. Character states: stomata, – absent, + present; seta, s straight, f flexuous, c cygneous; annulus, + complex and revoluble, – simple and adherent; spores, p papillose, w warty; peristome, s striate-papillose, p papillose, i inserted at mouth, b on basal membrane.
Stomata Seta Annulus Spores Peristome
Dicranella – s/f +/– p/w s,i/b
Microdus – s + p/w p, i
Anisothecium + s/f – p s/p, b
Campylopodium + c + p s, i
(Not in Central America)
Microcampylopus – c + w s, i
Aongstroemia + s + p p, i