Gymnomitriaceae
Terrestrial or lithophytic, paroecious, autoecious (not in Victoria) or dioicous. Specialised asexual propagules absent. Stems simple to irregularly branched, mostly branched near base, mostly with two ranks of lateral leaves, erect with normal leaves and prostrate with microphylls or sometimes with normal leaves (not in Victoria), sometimes completely prostrate (not in Victoria); branches emerging from main stem near lateral leaves and with or rarely without a collar of tissue at base. Lateral leaves incubous to succubous, alternate, imbricate, especially toward stem apex, contiguous or distant, erect-appressed to loosely spreading (not in Victoria), rarely squarrose (not in in Victoria), ovate to oblong or orbicular (not in Victoria) in outline, concave adaxially, bilobed or rarely trilobed (not in Victoria) or unlobed (not in Victoria); lobes entire or crenulate, but often erose with age, rounded, acute or setaceous (not in Victoria). Underleaves rarely present (not in Victoria) and few-celled or lanceolate to linear and much narrower than stem, free or slightly fused at base on one side to adjacent lateral leaf. Leaf cells circular to elliptic or quadrate to oblong, smooth or papillose, thin-walled with distinct trigones throughout or toward base and evenly thick-walled toward margins, or evenly thick-walled throughout (not in Victoria), with 2–6 spherical or ovoid to ellipsoid and homogenous (not in Victoria), finely granular or granular-botryoidal (not in Victoria) oil bodies, rarely completely absent (not in Victoria), sometimes becoming hyaline and without oil bodies near margins (not in Victoria). Rhizoids scattered on prostrate stems, without internal peg-like thickenings, colourless. Androecia on leading stems, with up to 12 pairs of leaf-like but often larger and more ventricose bracts, each with 1–6 antheridia. Sporophyte at apex of leading stem, rarely on short lateral branch (not in Victoria), surrounded by bracts and with or without a highly reduced perianth; bracts similar to normal vegetative lateral leaves but larger, sometimes those closest to sporophyte with dentate to lacerate margins, those closest to sporophyte abruptly reduced in size to bractlets when perianth absent; perianth when present concealed by bracts or rarely slightly emergent from bracts (not in Victoria), sometimes terminal on perigynium, tubular or ovoid, plicate and crenulate at mouth, with age sometimes becoming dissected; perigynium when present ring-like or tubular, rarely bulbous basally forming a marsupium precursor (not in Victoria). Capsule spherical to ovoid, 2–3-stratose, dehiscing by 4-valves, barely emergent beyond bracts when fully mature; elaters 2–4-spiral. Spores spherical, smooth to granulate, brown.
Nine genera attributed to this family by Söderström et al. (2016), but at least two monotypic genera misplaced (Váňa et al. 2010), leaving 83 remaining species; two genera and species in Victoria.
The limits of the Gymnomitriaceae requires confirmation and it is likely that it will continue to change once additional genera are included in phylogenetic analyses of DNA sequences (Váňa et al. 2010). The Gymnomitriaceae previously included two genera, Herzogobryum Grolle and Nothogymnomitrion R.M.Schust., with well-developed and conspicuous perianths, but have been removed from this family based on their distant placement in the suborder Cephaloziineae in phylogenies based on multiple DNA regions (Shaw et al. 2015). Most of the remaining taxa have a highly reduced or no perianth, however, Nardia S.F.Gray, which has a well-developed perianth, was also shown to belong to the Gymnomitriaceae (Shaw et al. 2015), demonstrating that the degree of perianth development varies considerable within this family and cannot be used solely as a defining feature.
Gymnomitriaceae mostly occur in alpine and subpolar climates. The often tightly imbricate leaves, dense cushion growth form and often decolorate exposed leaf margins provide adaptations to surviving harsh conditions in these climates such as high UV exposure, desiccation and freezing (Schuster 1996, 2002).
Schuster, R.M. (1996). Studies on Antipodal hepaticae. XII. Gymnomitriaceae. Journal of the Hattori Botanical Laboratory 80: 1–147.
Schuster, R.M. (2002). Austral Hepaticae Part II. Nova Hedwigia Beiheft 119. Cramer in der Gebrüder Borntraeger Verlagsbuchbehandlung: Berling & Stuttgart.
Shaw, B., Crandall-Stotler, B., Váňa, J., Stotler, R.E., von Konrat, M., Engel, J.J., Davis, E.C., Long, D.G., Sova, P. & Shaw, A.J. (2015). Phylogenetic relationships and morphological evolution in a major clade of leafy liverworts (Phylum Marchantiophyta, Order Jungermanniales): Suborder Jungermanniineae. Systematic Botany 40: 27–45.
Söderström, L., Hagborg, A., von Konrat, M., Bartholomew-Began, S., Bell, D., Briscoe, L., Brown, E., Cargill, D.C., Costa, D.P., Crandall-Stotler, B.J., Cooper, E.D., Dauphin, G., Engel, J.J., Feldberg, K., Glenny, D., Gradstein, S.R., He, X., Heinrichs, J., Hentschel, J., Ilkiu-Borges, A.L., Katagiri, T., Konstantinova, N.A., Larraín, J., Long, D.G., Nebel, M., Pócs, T., Puche, F., Reiner-Drehwald, E., Renner, M.A.M., Sass-Gyarmati, A., Schäfer-Verwimp, A., Moragues, J.S., Stotler, R.E., Sukkharak, P., Thiers, B.M., Uribe, J., Váňa, J., Villarreal, J.C., Wigginton, M., Zhang, L. & Zhu, R. (2016). World checklist of hornworts and liverworts. Phytokeys 59: 1–828.
Váňa, J., Söderström, L., Hagborg, A., von Konrat, M. & Engel, J.J. (2010). Early land plants today: Taxonomy, systematics and nomenclature of Gymnomitriaceae. Phytotaxa 11: 1–80.
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