Orthotrichum Hedw.

Plants small or robust, dark green, brown-, yellow-green, or rarely black, dull, mostly forming tufts (rarely small mats) on bark or rock. Stems erect, ascendant, or rarely creeping, branching by innovation or occasionally forking, in cross-section lacking a central strand, beset below with smooth, mostly brown rhizoids. Leaves erect, incurved or rarely contorted when dry, spreading or erect-spreading when moist, ovate-lanceolate, narrowly lanceolate, oblong-lanceolate, or rarely ligulate-lanceolate, acute, acuminate, or obtuse, plicate or not, entire; margins mostly recurved or revolute, rarely plane; mid and upper laminal cells rounded to ± hexagonal, ± isodiametric, thick-walled, usually unistratose, rarely 2–(3–4)-stratose and opaque, mostly pluripapillose on both surfaces, rarely only slightly papillose or smooth; basal interior cells rectangular, rhomboid, or rarely ± quadrate, thick- or thin-walled, porose or not, often coloured; cells of basal margins often shorter and extending up the margins, but not forming a distinct hyaline border; alar cells not differentiated. Costa mostly failing below the leaf apex, in cross-section with no differentiated guide cells or stereids. Gemmae occasionally present on leaves.

Autoicous (often gonioautoicous) or rarely dioicous. Perichaetia terminal, with perichaetial leaves not or slightly larger than vegetative leaves. Perigonia often gemmiform and immediately below the perichaetia. Setae one to several per perichaetium, straight, slender to stout, very short to elongate, smooth; capsules emergent, immersed, or exserted, erect and symmetric, ovoid-cylindric, subcylindric, broadly ovoid, or rarely nearly globose, mostly striate and furrowed (especially when dry) but sometimes smooth; exothecial cells often in alternating bands of thick- and thin-walled (the thicker-walled cells corresponding with ribs in dry capsules) and variably pigmented cells, with several rows ± oblate and thicker-walled at mouth; stomata superficial or immersed, variably distributed in the capsule wall (not restricted to neck); annulus absent or poorly developed; operculum short-rostrate (rarely obliquely so) from a conic or convex base. Peristome double, single, or rarely absent, with 16 (but often paired) teeth which are variably papillose or striate, and recurved, spreading, or almost erect when dry; preperistome present or absent; endostome, if present, lacking a basal membrane and composed of 8 or 16 filiform segments which alternate with the teeth. Calyptra campanulate-mitrate, hairy or naked. Spores extremely variable, either isosporous or anisosporous, unicellular or multicellular, variable in shape and size.

Orthotrichum is a large genus of temperate distribution in both northern and southern hemispheres. Lewinsky (1993) considered it to consist of 116 species distributed in seven subgenera (but she did not fuse Muelleriella with Orthotrichum). The genus is interpreted more broadly here to include the species placed by Sainsbury (1955) and by Vitt (1976) in the genus Muelleriella. Twelve species (six endemic) and two varieties (both endemic) are accepted as part of our flora. Orthotrichum cupulatum var. austro-cupulatum, which Lewinsky recognised, is not accepted here.

Orthotrichum is a taxonomically difficult genus growing on trees and shrubs and on rock. With a few exceptions, the N.Z. species of Orthotrichum cannot be confidently recognised without microscopic examination. Characterisation of the stomata (whether superficial or immersed, etc.) is facilitated by making a longitudinal section of a mature capsule in 95% ethanol. The ethanol will serve as a spore dispersant and facilitate visualisation of the stomata. Transferring the sectioned capsule between ethanol and water repeatedly will further disperse the spores. Until one is very well acquainted with the regional flora, microscopic examination of the stomata is recommended, as species with superficial and immersed stomata can be very similar in appearance.

Orthotrichum (in a traditional taxonomic sense) was masterfully treated by Lewinsky (1984) for Australasia. However, for reasons given below, the genus is treated here in a broader sense than by Lewinsky. For most of the included species, the treatments here are derived, with permission, from Lewinsky’s elegantly illustrated revision. In CHR and WELT Lewinsky typically named and isolated all the species found in single collections. Her meticulously annotated segregates within single herbarium specimens are a valuable resource for anyone seriously wishing to come to grips with this difficult genus regionally.

Lewinsky (1984, p. 395) stated that the Australasian Orthotrichum flora differed from that of North America and Europe by having a smaller fraction (only three of the 11 taxa treated by her) of taxa with immersed stomata; by contrast 11 of 19 British species recognised by Smith (2004) have immersed stomata. Lewinsky-Haapasaari & Ramsay (2006) noted that of the five species occurring in Australia, all those with immersed stomata have the chromosome number n = 6, while those with superficial stomata have n = 11.

Lewinsky (1984) provided detailed distribution maps and a summary of the substrate preferences (see her Table 1) for all taxa. Among the introduced woody plant genera Fraxinus, Populus, and Salix support the greatest diversity of species. The N.Z. distributions and ecological notes presented by Lewinsky form the basis of those given below, but they have been confirmed and expanded where possible using herbarium specimens in AK, CHR, and WELT. Many of Lewinsky’s records seem to be derived from her painstaking determinations of multiple species within herbarium collections. The species descriptions below are largely modified from those of Lewinsky (1984).

Goffinet et al. (2004) used molecular data from four ribosomal, mitochondrial, and nuclear loci to evaluate relationships among the subfamily Orthotrichoideae; Orthotrichum is presented here in the broader sense dictated by their conclusions. The species traditionally placed in the segregate genus Muelleriella (Brotherus 1925) can be distinguished from Orthotrichum s.s. by several morphological features, including multicellular spores, a single peristome with a well-developed preperistome, multistratose leaf lamina, and nearly black colour. These species are also specialised in terms of habitat and are almost exclusively found on coastal rocks, often those exposed to extensive salt spray, in austral regions. Lewinsky (1993) argued in favour of the continued recognition of Muelleriella. However, the evidence provided by Goffinet et al. (2004) supporting the inclusion of Muelleriella within Orthotrichum seems incontrovertible. Interestingly, Goffinet’s inclusion of Muelleriella within Orthotrichum accords with the treatment of Dixon (1926, p. 170), who included a group "Crassifolia" of unspecified rank. The taxa previously assigned to Muelleriella clearly comprise a natural and probably monophyletic subgroup within Orthotrichum.

A synopis of the systematic relationships Lewinsky (1993) accepted for Australasian taxa of Orthotrichum s.s. (excluding the species sometimes placed in Muelleriella) is presented below.

Species of Orthotrichum can usually be differentiated from Ulota by having less crisped leaves when dry, much less thick-walled (especially the transverse walls) marginal basal laminal cells of the leaves, and by stomata that are either superficial or immersed and not confined to the capsule base. In Ulota the stomata are invariably superficial and confined to the capsule base. Orthotrichum calvum is the one species most likely to be misidentified as a species of Ulota.