Lithophytic, terrestrial, on logs or epiphytic (not in Victoria), dioicous. Asexual reproduction by 1–2-celled gemmae produced at stems apices (not in Victoria) or (not in Victoria) intercalary on leafy or leafless stems. Stems differentiated into leafless creeping axes and erect unbranched or sparingly branched leafy axes; branches emerging from main stems near lateral leaf or from ventral side of stem and with a collar of tissue at base, or rarely near abaxial side of lateral leaf and without a collar of tissue at base. Lateral leaves orbicular, reniform, elliptic (not in Victoria), lingulate (not in Victoria), obovate (not in Victoria) or broadly ovate, asymmetric, unlobed or rarely bilobed (not in Victoria), succubous, vertically oriented and sometimes secund in direction of abaxial stem or erect-spreading to widely spreading perpendicular to the stem (not in Victoria), alternate, remote to imbricate, entire, denticulate, dentate or bidentate (not in Victoria), incurved along basiscopic margin or plane. Underleaves absent. Leaf cells oblong, polygonal or irregular, usually becoming more elongated toward base, smooth, thin- to thick-walled, without distinct trigones, with 3–14 oil bodies; oil bodies spherical, obloid or ovoid, granular-botryoidal, colourless. Rhizoids sparse and confined to creeping leafless stems. Androecia forming short branches arising from near leafy stem bases or from leafless creeping stems, with 4–6 pairs of ventricose bracts, each with a single antheridium. Sporophytes terminating short branches without normal leaves arising from near leafy stem bases or from leafless creeping stems often developing within differentiated bracts, rarely within a perianth (not in Victoria) or perianth absent and its role replaced by a shoot calyptra; bracts unlobed or 2–3-lobed; shoot calyptra green, fleshy, clavate to obovoid; perianth absent or (not in Victoria) rarely present and ovoid, trigonous and with irregularly denticulate to ciliate mouth; capsule ellipsoid, 4–6-stratose; elaters bispiral; spores vermiculate or granulate (not in Victoria).

Eleven species with around half shared between moist southern temperate regions and oceanic islands and Subantarctic islands, and half in tropical mountainous areas of the Americas north to Mexico and the Caribbean, but with disjunct occurrences in Ireland and the mountains of East Africa (Schuster 2002; Söderström et al. 2016); one species, A. falcatus (Hook.) Mitt., in Victoria.

Scott (1985) recognised two species of Adelanthus in Victoria. These are now considered to belong to two separate genera. Adelanthus has been applied to both these genera due to a species from each of these genera being considered the type species of Adelanthus. Mitten (1864) originally described Adelanthus as having perianths that are bluntly trigonous and narrowed to a dentate apex, and included the species A. falcatus (Hook.) Mitt., A. magellanicus (Lindenb.) Mitt., A. lindenbergianus (Lehm.) Mitt. and A. decipiens (Hook.) Mitt. (as A. dicipiens). Mitten (1864) did not designate a type species for the genus, and Schuster (1967, 2002) interpreted the statement ‘Adelanthus was founded by Mr Mitten in 1864, for the reception of Jungermannia decipiens of Hooker’ by Spruce (1876) as the first typification and suggested that the only logical choice of a type for Adelanthus that matches the description of having a perianth would be A. decipiens. This is because perianths on A. lindenbergianus were ‘yet unknown’ to Mitten and A. falcatus never produces a perianth, despite Mitten believing that they do based on their superficial resemblance to Plagiochila that have perianths. Mitten (1864) attributed the absence of perianths in A. falcatus to their fragility and decay. It is possible that A. magellanicus is an Adelanthus with a perianth, but based on the synonymy and cited specimens it is clear that Mitten (1864) included multiple species within his A. magellanicus and the perianth described may not have pertained to the Adelanthus element, but instead possibly a Plagiochila species.

Adelanthus Mitt. was conserved by A.W. Evans in Camp et al. (1949) against the earlier published Adelanthus Endl. (synonymous with the flowering plant genus Pyrenacantha Baill.), unfortunately designating the type as A. falcatus. Grolle (2003) clarified that A. falcatus should continue to be considered the type of Adelanthus because according to Art. 14.8 of the International Code of Botanical Nomenclature changing the type of a conserved name can only occur by acceptance by committee of a proposal to replace the listed type, published in the journal Taxon, which has not yet occurred. If the name was not conserved, Adelanthus decipiens could be used as the type according to Art. 9.19 that outlines that the designated type (in this case a lectotype) can be superseded if it is in serious conflict with the protologue. If an original designation of A. decipiens as type by Spruce (1876) is accepted as claimed by Schuster (1967), changing the type to A. falcatus when conserving Adelanthus Mitt. is permitted according to Art. 14.9 that states that ‘a name may be conserved with a different type from that designated by the author or determined by application of the Code’.

The two genera considered as Adelanthus have been confirmed as forming separate lineages in phylogenetic analyses of DNA sequences (Feldberg et al. 2010). Adelanthus (including A. falcatus) comprises the species that have leaf cells without distinct trigones that usually become more elongate toward the leaf base, usually produce gemmae on the stem and that usually lack perianths. Calyptrocolea R.M.Schust. is synonymous with this genus (Schuster 2002). The other genus, Pseudomarsupidium Herzog, which Schuster (2002) treated as Adelanthus, has isodiametric cells with distinct trigones that do not become strongly elongated basally, do not produce gemmae and form a perianth to some degree. This genus is most closely related to Wettsteinia Schiffn., confirming its distinction from Adelanthus (Feldberg et al. 2010).

Camp, W.H., Rickett, H.W. & Weatherby, C.A. (1949). Proposed changes in The International Rules of Botanical Nomenclature. Brittonia 7: 1–51.

Feldberg, K., Váňa, J., Long, D.G., Shaw, A.J., Hentschel, J. & Heinrichs, J. (2010). A phylogeny of Adelanthaceae (Jungermanniales, Marchantiophyta) based on nuclear and chloroplast DNA markers, with comments on classification, cryptic speciation and biogeography. Molecular Phylogenetics and Evolution 55: 293–304.

Grolle. R. (2003). On the typification of Adelanthus Mitt. (Marchantiopsida: Adelanthaceae). Journal of Bryology 25: 215–216.

Mitten, W. (1864). A new genus of Hepaticae. Journal of the Linnean Society 7: 243–244.

Schuster, R.M. (1967). On Adelanthus Mitten: a case of the International Rules versus the International Rules. Nova Hedwigia 12: 353–361.

Schuster, R.M. (2002). Austral Hepaticae Part II. Nova Hedwigia Beiheft 119. Cramer in der Gebrüder Borntraeger Verlagsbuchbehandlung: Berling & Stuttgart.

Scott, G.A.M. (1985). Southern Australian Liverworts. Australian Government Publishing Service: Canberra.

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.

Spruce, R. (1876). On Anomoclada, a new genus of Hepaticae, and on its allied genera, Odontoschisma and Adelanthus. Journal of Botany, British and Foreign 5: 129–136, 161–170, 193–203, 230–235.

Myriophyllum gracile