Zygodon Hook. & Taylor

Elements in the following description are taken from Crum & Anderson (1981) and Vitt (1994).

Plants small to robust, forming tufts or turves, mostly on bark or rock, dull or weakly lustrous, green, brown, yellow-brown, or red-brown. Stems erect or ascendant, simple, forked, or branched by innovation, usually covered with dense red-brown or pale brown and papillose rhizoids, in cross-section with small incrassate cortical cells, thick-walled internal cells, and lacking a central strand. Leaves imbricate, erect, and often contorted when dry, erect-spreading to reflexed when moist, often undulate, ovate to linear-lanceolate or ligulate, mostly acute to acuminate, entire or ± toothed near apex (sometimes crenulate from projecting papillae), keeled, with margins mostly plane, occasionally recurved below; upper laminal cells rounded-hexagonal to subquadrate, firm-walled, smooth or pluripapillose (occasionally unipapillose) on both surfaces, sometimes arranged in neat oblique rows; basal cells rectangular or linear, less papillose or smooth, thinner-walled, often ± yellow; alar and marginal cells not differentiated. Costa prominent, smooth throughout or papillose abaxially above, ending below apex to excurrent. Gemmae borne in clusters on axillary stalks or on rhizoids, usually numerous, clavate to cylindric, and transversely (and rarely longitudinally) septate. Laminal KOH colour reaction positive, yellow or occasionally red, rarely absent.

Sexuality various. Male and female plants mostly similar, rarely dimorphic. Perichaetia terminal, the leaves not or only weakly differentiated. Perigonia often gemmiform, terminal (but often becoming lateral by innovation). Setae terminal, ± elongate, ± yellow, smooth; capsules exserted, erect and symmetric, subcylindric to obovoid, to narrowly pyriform, with a long neck, strongly 8-furrowed; exothecial cells in alternate longitudinal bands of thick-walled and thin-walled cells; stomata superficial, restricted to the neck and lower urn; annulus weakly differentiated or apparently lacking; operculum long-rostrate, often oblique, from a conic base. Peristome single (then endostomal), double, or none; exostome teeth united to form 8 pairs, at least when young, papillose or papillose-striate, recurved or erect when dry; endostome segments (if present) 8 or rarely 16, slender and linear, variably ornamented, arising from a low basal membrane. Calyptra cucullate, naked, smooth or papillose near the apex. Spores globose, small, unicellular.

Malta’s (1926) revision of the genus remains extremely useful. Lewinsky’s (1990) beautifully illustrated revision of Zygodon for Australasia provides an introduction to many aspects of the genus, including its history. This treatment provided the basis for Lewinsky-Haapasaari & Ramsay’s (2006) treatment of the genus in the Flora of Australia. The taxonomy presented in these two treatments is mostly followed here, with the notable exception that one Australasian species is placed in the segregate genus Leratia Broth. & Paris, following the analysis of Goffinet et al. (2004). Further information about some N.Z. species may be found in Calabrese’s (2006) well-illustrated revision of southern South American species.

The arguments presented by Goffinet & Vitt (1998) and Goffinet et al. (2004) in favour of resurrecting the genus Codonoblepharon are not accepted here. Zygodon menziesii (Schwägr.) Arn., the type species of the genus Codonoblepharon, and other N.Z. species with smooth laminal cells are retained here in Zygodon, as advocated by Lewinsky. Those interested in this segregate genus are referred to the writings of Goffinet and co-authors, and to Matcham & O'Shea (2005).

Goffinet & Vitt (1998) placed Zygodon and its close allies (including Codonoblepharon) in the tribe Zygodonteae.

Zygodon is a large genus distributed in all temperate and tropical regions. Smith (2004) considered Zygodon to be a genus of c. 50 spp. worldwide; six species are accepted for N.Z.

The species descriptions of Zygodon spp., and the following key to species, are modified from Lewinsky (1990), whose revision of the Australasian representatives provides the base line for our regional understanding of this genus.

Zygodon anomalous Dozy & Molk. was applied by Dixon (1926, p. 164) to the N.Z. material recognised here under the name Z. hookeri. On p. 365, Dixon cited Malta’s (1926) opinion that this name is founded on disparate elements. Lewinsky (1990) considered Z. anomalous to be a nom. dub. and rejected its application to N.Z. material; her views are accepted here.

Zygodon obtusifolius Hook. is here considered under the genus Leratia.

Zygodon reinwardtii (Hornsch.) A.Braun has been applied to N.Z. material by various authors, including Wilson (1854). Dixon (1926, p. 164) discussed the name Z. reinwardtii in relation to N.Z. material at some length and rejected its use. Lewinsky (1990) differentiated the widespread (predominantly southern Asian and Latin American) Z. reinwardtii from the Australasian Z. hookeri by the former’s "more strongly dentate leaf margins and the more pronounced nerves which are widened towards the apex and excurrent in nearly all leaves" and by the nature of their gemmae. Her views are accepted here and this species is not discussed further.