Bryum laevigatum Hook.f. & Wilson

Plants brown- or yellow-green, mostly robust but extremely variable in size, forming loose or compact turves. Stems branching by innovation, (5–)25–50 mm (but to c. 100 mm in aquatic situations), beset with dark brown, coarsely gemmate-insulate or baculate rhizoids below, in cross-section with firm-walled cortical cells and a distinct central strand, sometimes scalloped in outline. Leaves evenly spaced on stem, mostly erect-spreading when moist, variably contorted when dry, oblong-spathulate, oblong-elliptic, to broadly elliptic (broadest at or above mid leaf), tapered to a broadly acute or obtuse and sometimes cucullate apex, narrowed at insertion, highly variable in size, mostly 1.6–2.8 mm on vegetative stems, concave or occasionally subtubulose, usually red-brown at base, entire or serrulate near apex, variably bordered, recurved to shoulder or plane; upper laminal cells rhombic or ± hexagonal-rhombic, very incrassate and slightly more so in corners, weakly porose, variable in dimensions, mostly 25–50 × 12–25  µm and 2–3:1, ± obliquely oriented, usually becoming shorter in extreme apex, becoming longer, more hexagonal, and more porose below and often ± oblong near the leaf base; marginal cells weakly to well-differentiated, forming an ill- or well-defined border 1–5 cells wide at mid leaf but not extending to leaf apex; basal cells mostly red-brown, sometimes with a large but ill-defined area of ± quadrate cells in alar angles. Costa stout, pale brown (mostly darker or ± red below), subpercurrent, percurrent, or very short-excurrent, in cross-section strongly projecting abaxially, round, and with a single layer of guide cells abaxially, plane or weakly convex and with 1–2 rows of guide cells adaxially, with a very large central stereid group. Brood bodies (including tubers) absent.

Perichaetia scattered on main stem (and overtopped by subperichaetial innovations), with perichaetial leaves distinctly enlarged, ± oblong-deltoid, c. 3.2–4.0 mm. Perigonia inconspicuous, terminal or becoming lateral by innovation, with outer bracts not distinguished from vegetative leaves, the inner bracts smaller, broadly ovate, brown below, enclosing numerous antheridia and brown, filiform, 7–8-celled paraphyses. Setae to c. 30 mm; capsules subpendent or pendent, obovoid-cylindric, 3.5–4.5 mm long, with an ill-defined neck less than ⅓ the total capsule length, only weakly constricted below mouth when dry; operculum conic, apiculate in N.Z. material. Exostome teeth yellow-brown throughout, connate at base; endostome with perforate segments ± equal the teeth in length and well-developed appendiculate cilia mostly in groups of 3. Spores (12–)16–18 µm, nearly smooth.

Seppelt 2004, fig. 40; Spence & Ramsay 2006, fig. 40 P–W (as Gemmabryum laevigatum).

A species of extremely wide habitat tolerance, best developed in damp situations such as stream margins, seepages, lake margins, but also common in drier situations on rock or thin soil. Occurring on mineral or humic soil over a variety of rock types (including limestone, gneiss, greywacke, and mortar), on alluvial sand, and eroding soil banks, in both insolated and ± shaded situations. Ranging from near sea level to c. 2300 m. Commonly associated mosses include Breutelia pendula, Bryum pseudotriquetrum, Cratoneuropsis relaxa, Drepanocladus aduncus, Fissidens rigidulus, Ochiobryum blandum, Philonotis tenuis, and Tridontium tasmanicum.

Bryum laevigatum is extremely variable in respect to stature, leaf shape, size, degree of contortion when dry, and degree of leaf margin recurvature. The most reliable diagnostic features of this non-comose but robust species are the very thick-walled laminal cells that are both porose and ± obliquely oriented and the stout, ± percurrent, brown costa that projects strongly abaxially from the dry lamina. Leaf dimension and shape can vary greatly even in single plants, especially when the plants are subject to periodic flooding (as in the type of B. huttonii). Shorter and broader leaves are often characteristic of plants from moister habitats. The occurrence of strongly recurved leaf margins does not seem correlated with moisture availability.

The degree of leaf contortion in dry material varies greatly, with most populations (including the type) having leaves turned to one side and the apices often ± incurved when dry. Dry leaves may also be weakly twisted about their own longitudinal axes. In many populations, however, there is little or no leaf contortion on drying.

Some populations have leaf margins strongly reflexed when dry and this, together with abaxially protruding costa, give the plants a distinctive appearance. Reflexed margins are not a constant feature of this species, however, and the utility of this feature as a recognition aid is given too much emphasis by Scott & Stone (1976, p. 282). In the species type, the leaf margins are plane or even slightly incurved when dry. A curious feature of this commonly fruiting species is the apparent rarity of perigonia.

The type sheet of B. laevigatum (BM-Wilson) consists of five packets of the same collection attached to a single sheet, with several Wilson drawings dated between 1844 and 1854 and a single packet of Gunn 1588. The packet at extreme upper right corner of the sheet (BM 730494) bears the collection number Lawrence 261 (in pencil, in the hand of neither J.D. Hooker nor W. Wilson). The selection of this material as lectotype conforms with the protologue and with Ochi's (1970, p. 42) designation of "Hooker 2856" as isotype of this name. The number 2856 is a Hooker herbarium number and not a collection number per se as indicated by Spence & Ramsay (2006). The several packets in the Wilson herbarium also preclude considering any of the packets as a holotype, as done by Spence & Ramsay.

Type material of B. incurvifolium Müll.Hal. has been seen only online (at JSTOR Global Plants, accessed 15 Jan. 2015), however the online photograph of E2442 in my opinion is sufficiently detailed to permit confident placement of this name in the synonymy of the widespread B. laevigatum. Material referred by Dixon to B. incurvifolium Müll.Hal. has also been examined and referred to B. laevigatum.

The lectotype of B. crassinerve is designated (by Wilson) by a symbol of two dots under a dash and bears Wilson's annotation "specimen drawn, March 10, 1852." The lectotype, collected by Sinclair, is mounted at the right hand margin of a sheet in Wilson's herbarium, immediately below Wilson's drawings of Colenso 4785. In the upper left hand corner of the relevant sheet are Wilson's drawings of March 10, 1852. Wilson's handwritten draft protologue is mounted on another sheet, with several duplicates of a Hooker collection.

No type material of B. eximium Mitt. has been available for study. However, material collected by D. Petrie at Dunedin (CHR 516747) and determined by Brotherus as B. eximium, is unquestionably the same aquatic form of B. laevigatum as the type of B. megamorphum Müll.Hal. On this basis, plus Dixon’s (1926, p. 217) comment that "this remarkably fine plant [B. eximium] will … have to be looked upon as a striking marsh form of B. laevigatum", B. eximium is considered here a synonym of B. laevigatum. Apparent syntype material of B. eximium (in the Mitten herbarium at NY) has been viewed at JSTOR Global Plants (accessed 15 Jan. 2015) but little morphological detail can be seen in the online photographs.

Plants of a submerged population of B. laevigatum were described by Müller under the name B. megamorphum. The type of this name is (compared to terrestrial forms of B. laevigatum) more lurid brown with elongate (to c. 130 mm) stems; its leaves are more distant, widely spreading, broader and more obtuse, less concave, much larger (to c. 6 × 3 mm), weakly and bluntly serrate above, and more weakly recurved. Also, its upper laminal cells are less incrassate, more porose, and decidedly less obliquely oriented and its costae are narrower and protrude abaxially less prominently when dry. In addition to the type, the best examples of the "megamorphum growth form" are from the Dunedin area, but similar material has been seen from other N.Z. regions. Transitional forms from subaquatic habitats, with distant leaves that are larger than the usual range for the species are not uncommon (e.g., CHR 464913 ex Mt Arthur, Nelson L.D.). The collector of the type, W. Bell, referred to B. megamorphum (in herb. Beckett) as "The Emperor of all the New Zealand Bryum".

Material (in CHR, WELT) cited as B. muehlenbeckii by Bartlett (1984) from the Ruahine and Mt Arthur Ranges, and accepted by Fife (1995), is here referred to B. laevigatum. It is probable that reports of B. muehlenbeckii from Australia (e.g., Crum & Anderson 1981, p. 564) are also based on other misdeterminations of B. laevigatum. Confusion sometimes occurs between B. laevigatum and B. pseudotriquetrum, q.v. Specimens that cannot be confidently assigned to either B. laevigatum or Rosulabryum subtomentosum rarely occur (e.g., CHR 467597 ex Ruahine Range). When sterile, plants of Pleurophascum ovalifolium can be strikingly similar to B. laevigatum, however the former differs in many ways including its obvious lack of costae, and its areolation and rhizoid colour.