North America, Mexico, West Indies, South America, Europe, Asia, Africa, Pacific Islands, Australia.
Genera 2, species 5 (2 genera, 5 species in the flora).
Aulacomniaceae are found in the Northern Hemisphere including the high Arctic region, and sporadically in the Southern Hemisphere. Leptotheca Schwägrichen was long included in Aulacomniaceae (V. F. Brotherus 1924), but peristome and gametophytic structure (S. P. Churchill and W. R. Buck 1982), as well as molecular evidence (N. E. Bell et al. 2007), indicate affinities elsewhere (with Rhizogoniaceae, Churchill and Buck; or Orthodontiaceae, B. Goffinet et al. 2008). The molecular results of Bell et al. joined Aulacomnium, Hymenodontopsis Herzog, and Mesochaete Lindberg in a newly recognized Aulacomniales. Goffinet et al. placed these three genera in Aulacomniaceae (Rhizogoniales). In molecular phylogenies (Bell and A. E. Newton 2004; T. J. O’Brien 2006), Mesochaete, a genus of two species in eastern Australia (I. G. Stone 1983), one of which is also on Lord Howe Island, is sister to Aulacomnium in the broad sense (Bell and Newton; O’Brien).
Aulacomniaceae as treated here consists of two genera: Arrhenopterum (a monospecific genus usually included in Aulacomnium) and Aulacomnium, in the strict sense. T. J. O’Brien (2006) presented molecular evidence that Arrhenopterum (as Aulacomnium heterostichum) and other species in Aulacomnium that he studied are sister groups. Additional molecular and morphological studies are likely to alter the family circumscription.
|1||Leaves lanceolate, oblong-lanceolate, linear-lanceolate, or oblong-elliptic, spirally arranged, symmetric; bases tapered, scarcely tapered, or slightly rounded to insertion, broad; margins often irregularly serrulate at apex; laminal cell papillae prominent, abaxial and adaxial cell surfaces plane to somewhat domed; sexual condition dioicous.||Aulacomnium|
|1||Leaves oblong-ovate, ± complanate, often asymmetric; bases abruptly rounded to insertion, narrow; margins strongly serrate distally; laminal cell papillae weakly developed or absent, abaxial and adaxial cell surfaces bulging; sexual condition autoicous.||Arrhenopterum|