Bryum Hedw.

Plants small to robust, extremely variable in size and coloration, forming turves or tufts, terrestrial or occasionally epiphytic. Stems from a few millimetres to several centimetres, mostly red-brown, usually strongly beset with rhizoids, in cross-section with firm-walled cortical cells and a well-developed or rarely weak central strand of smaller thinner-walled cells. Leaves evenly spaced on stem or crowded and enlarged at stem apex (comose), erect or erect-spreading when moist, round, elliptic, ovate, or lanceolate, acute, acuminate, or rarely rounded at apex, ± concave, not complanate, often with secondary pigments, toothed or entire, bordered, recurved or less often plane, sometimes decurrent; upper laminal cells hexagonal or rhombic-hexagonal, thin- or firm-walled, porose or not, becoming more oblong in lower leaf; marginal cells differentiated, linear, usually forming a strong or weak border. Costa strong, excurrent, percurrent or occasionally shorter, with a single abaxial stereid band. Brood bodies (gemmae, tubers, or bulbils) often present.

Dioicous or monoicous. Perichaetia terminal on main shoot or on short shoots arising near the stem base, very often overtopped by subperichaetial innovations (and thus appearing lateral); perichaetial leaves mostly moderately differentiated. Perigonia with numerous filiform paraphyses and antheridia. Setae elongate, flexuose to cygneous, one per perichaetium in N.Z. species; capsules cernuous, pendent or rarely suberect, variable in form, mostly pyriform, clavate, cylindric, or rarely ± globose, mostly with a well-developed neck, straight or curved; stomata numerous, superficial, and restricted to neck; annulus well developed and revoluble; operculum conic, sometimes apiculate. Peristome double and often perfect; exostome teeth yellow-brown or pale, finely papillose below and mostly hyaline and baculate above, bordered, densely trabeculate on adaxial surface; endostome with a high basal membrane, with well-developed, perforate or fenestrate segments, and with cilia in groups of 1–3, appendiculate, nodose, or occasionally reduced or absent. Calyptra cucullate and smooth. Spores spherical and nearly always <30 µm.

Bryum is one of the largest and taxonomically most difficult genera of mosses. While some estimates of its size extend to 800 species (Brotherus 1924), or even to c. 1050 species (Smith 1978), such estimates are probably excessive. Ochi (1992), a noted authority on the genus, estimated the genus to include c. 180 or more species distributed worldwide. Twenty-four species are accepted for N.Z. in this treatment. A useful treatment of the genus for Australasia was provided by Ochi (1970, 1973, 1984). Ochi also (1992) provided an extremely useful synopsis of his classification of the Bryaceae, to which the interested student is referred. Because of rapidly changing concepts of the genus and its parent family, and lack of consensus on intra-generic relationships, no synopsis is presented here.

John Spence (often in association with Helen Ramsay) has proposed, in many publications, beginning with Spence (1987), radical changes in the classification of Bryum s.l. Spence & Ramsay (2006) assigned Australian species traditionally placed in Bryum to five genera while retaining only five Australian species within a narrowly circumscribed Bryum s.s. Their segregate genera are briefly discussed above; some of them under "Excluded Taxa" under the family treatment.

A comparatively conservative and enlarged view of Bryum is adopted here.

At its most highly-developed, the peristome in Bryum is sometimes termed "perfect". This terminology signifies a double peristome with the following characteristics: 1. exostome teeth with a distinct median zig-zag abaxial divisural line, finely papillose on the lower abaxial surface, mostly hyaline and baculate above, bordered, and densely trabeculate adaxially; and 2. an endostome arising from a high basal membrane, with well-developed, keeled, and perforate segments, and appendiculate cilia in groups of 1–3. This so-called "perfect peristome" (which is similar to that occurring in some Hypnum spp. and their allies) provides a reference point in the study of moss morphology. Characters of the peristome have historically been much used in the construction of moss classifications and only in recent years have they assumed a less important role, with the development of classifications based primarily on molecular characteristics.

The examination of peristome details is accomplished best by selecting a recently dehisced capsule and making a longitudinal cut through the peristome followed by a transverse cut slightly below the peristome insertion. The endostome (attached to the spore sac) usually then can be separated from the exostome using fine forceps. If spores obscure the peristomal structures, a drop of 95% ethanol will disperse the spores before the peristome is mounted in water. Treatment with ethanol also promotes the separation of the exostome and endostome, facilitating their dissection and observation. If no dehiscent capsules are available, peristome details often can be observed by removing the operculum from a nearly mature capsule by immersing the capsule in water on a microscope slide, adding a cover slip, and boiling gently, and sometimes repeatedly, causing the operculum to dehisce.

The variability of many of the species of Bryum makes identification of some material, especially if sterile, exceedingly difficult. Vegetative features are used to the greatest extent possible in the above key to NZ species. The key is intended as a guide to identification, but comparison to the descriptions, illustrations and, ideally, reliably determined specimens are often necessary for accurate identification. Many of our species have a distinct facies which permits their ready recognition. However, some of these features are difficult to incorporate into a conventional identification key. A fraction of Bryum collections will thus prove unidentifiable for even the most determined student. The initial collection of ample material with mature sporophytes is recommended for those wishing to become familiar with this genus. The production of an interactive key to regional representatives of Bryum would be a challenging and worthwhile project.

Many N.Z. Bryum spp. possess rhizoidal tubers in some populations and these can often facilitate species recognition. Tuber morphology is of particular taxonomic significance in the differentiation of species included in the "B. erythrocarpum complex" (see discussion under B. duriusculum). Examination of rhizoidal tubers may be accomplished by saturating a clump of several plants with water, and gently teasing apart the plant bases. Alternatively, tubers may be picked off the underside of a dry clod with damp forceps under a dissecting microscope. Where rhizoids are running adjacent to hard surfaces (e.g., a stone in the substrate) tubers are usually more abundant. Tubers can be sparse, even in species reputed to bear them consistently. Observations on tubers should be made in water mounts since some mounting media (notably Hoyer’s solution) alter their appearance, mainly by exaggerating the degree of cellular protrusions.

The recognised species are presented here in alphabetical order. However, a general discussion of the features of the distinctive "B. erythrocarpum complex" sensu Crundwell & Nyholm (1964) is given under the discussion of B. duriusculum, which is the most widespread member of the complex in N.Z. Six species of the "B. erythrocarpum complex" are accepted for N.Z.: B. duriusculum, B. radiculosum, B. ruderale, B. sauteri, B. rubens, and B. tenuisetum.

Although sharing features with other genera in either the Bryaceae or the Mniaceae (notably Brachymenium and Pohlia), the genus Bryum usually is easily distinguished by its rhombic-hexagonal laminal cells, mostly percurrent or excurrent costae, usually bordered and recurved leaf margins, and often cernuous or pendent capsules. Plants belonging to Pohlia generally have longer and narrower laminal cells and lack leaf borders, whereas Brachymenium (a genus not accepted for N.Z.) is predominantly epiphytic and more robust and has erect capsules with highly reduced endostomes.

A key to the N.Z. species of Bryum and its allied genera is presented above under the discussion of the family. In the descriptions, plant size definitions follow Ochi (1970, p. 14), and are based on the length of the largest stem leaves (including perichaetial leaves, but excluding the excurrent portion of the costa) as follows: robust, leaves >4.0 mm; large, leaves 3.0–4.0 mm; medium-sized, leaves 1.5–3.0; and small, leaves <1.5 mm.

Alternative keys to Australasian species of Bryum are provided by Ochi (1970) and Spence & Ramsay (2006).

The names Bryum affine Lindb. & Arn. and B. bimum Scherb. have been used as a "dumping ground" for several disparate species in N.Z. The correct application of these and other names associated with them has been the source of taxonomic and nomenclatural confusion for some time (see Dixon 1926, p. 207; Smith 1973; Smith 2004, p. 564; Crum & Anderson 1981, pp. 553–558). The resolution of this taxonomic and nomenclatural tangle (also involving B. creberrimum, q.v.) is beyond the scope of the present work.

The name Bryum chrysoneuron Müll.Hal. was applied by several N.Z. workers (including Dixon, Sainsbury, Allison, and Linzey) to at least three tuber-bearing species (B. duriusculum, B. sauteri, and B. clavatum). Ochi (1970) attempted to refine the application of the name B. chrysoneuron but was unable to locate type material (collected by S. Mossman "ad flumen Wairoa-river prope portum Kaipara" in 1850). The holotype was probably destroyed in the WWII burning of the Berlin herbarium. Efforts to locate potential type material for this name in other herbaria have failed. Given the lack of identifiable type material, and uncertainty surrounding the application of Müller's name, B. chrysoneuron is considered a nom. dub. and it is not applied in this work. A large proportion of the collections previously named as B. chrysoneuron are referable to B. duriusculum.

The highly variable Bryum microerythrocarpum Müll.Hal. & Kindb. has a Canadian type, is widespread in the northern hemisphere, and is recorded from N.Z. by Crundwell & Nyholm (1964). It is likely a later name for B. duriusculum Hook.f. & Wilson, which has a N.Z. type. The relationship between these two species is best examined in a monographic context and B. microerythrocarpum is not discussed further in this work.

The name Bryum obconicum Hornsch. was applied to N.Z. material by Hooker & Wilson (1854, p. 85). That name has been applied to numerous collections in N.Z. herbaria that are referred here to Rosulabryum capillare. Syed (1973, p. 318) considered much material named as B. obconicum Hornsch. to belong to B. torquescens Bruch. In this treatment Bryum obconicum is not accepted as a member of the N.Z. flora.