Fissidens Hedw.

Elements in the following description are taken from Pursell (2007).

Plants acrocarpous, minute (1–2 mm) to medium sized, to large in aquatic species (≥100 mm), gregarious, erect to decumbent, pale green to black, monomorphic or dimorphic, with distinct ventral and dorsal surfaces, complanate. Stems, except in the earliest stages, developing from a 2-sided apical cell, inclined, simple or branched, with branches often arising as innovations from below terminal gametoecia or from below damaged shoot apices; axillary hyaline nodules well-developed or otherwise; rhizoids smooth. Leaves distichous and strongly complanate, pinnately arranged on elongate stems or rarely palmate on short stems, usually overlapping but occasionally distant, plane to decurved, with a basal sheath (the vaginant laminae) equitant and inserted more or less horizontally; apex acuminate, acute or obtuse; vaginant laminae open to closed; dorsal lamina failing above the leaf base, ending at leaf insertion, or rarely, shortly decurrent on stem, tapered, truncate, or rounded at base; cells of apical and dorsal lamina thin- to thick-walled, smooth, unipapillose or multipapillose, flat to strongly bulging, generally more or less isodiametric; cells of vaginant laminae often larger, more elongate; marginal cells of laminae sometimes differentiated to form a border. Costa single, usually well-developed, rarely lacking or nearly so, failing below leaf apex to shortly excurrent.

Sexuality various. Perichaetia terminal or rarely lateral; perichaetial leaves often longer and/or narrower than vegetative leaves, with vaginant laminae open. Perigonia terminal or lateral, with leaves reduced, and with vaginant laminae concave and emarginate at their apex. Setae smooth, mostly elongate, erect, often geniculate at base, occasionally strongly hygroscopic; capsules erect to horizontal, symmetric or asymmetric, with stomata restricted to capsule base or rarely lacking; annulus lacking; operculum conic, usually rostrate. Peristome single, consisting of 16 teeth, usually divided in their distal region into 2 filaments. Calyptra smooth or occasionally scabrous, naked, mitrate or cucullate. Spores spherical to ellipsoid, smooth to finely papillose.

Fissidens is a very large genus. In his influential global review, Brotherus (1924) suggested that the number of Fissidens species approximated 700. Modern estimates are much lower, but still with some 450 species accepted world-wide by Crosby et al. (2000). Fissidens is regarded as one of the most successful moss genera (Pursell & Bruggeman-Nannenga 2004). For instance, among rheophytic mosses, Fissidens has the most members globally of any genus, and they are distributed on all continents except Antarctica (J.R. Shevock, pers. comm., 10 Feb. 2014).

Modern infrageneric classification of Fissidens is based on that of Müller (1848–1849; 1900), who recognised 12 groups within the genus. Improvements on Müller’s classification were made by Brotherus (1924), and subsequently by Norkett (1969). More recent refinements have been made by Bruggeman-Nannenga (1978), Iwatsuki & Inoue (1984), Pursell (1988), Bruggeman-Nannenga et al. (1994) and Pursell & Allen (1994). Changes have been made partly in response to newly recognised characters derived from detailed studies of peristomes with SEM (Mueller 1973; Allen 1980; Bruggeman-Nannenga & Berendsen 1990; Ishihara & Iwatsuki 1992). Additional techniques have included cytogenetic analysis (Iwatsuki & Inoue 1984), study of costal anatomy (Bruggeman-Nannenga 1990; Stone 1990b), and cladistic analysis of peristome types (Bruggeman-Nannenga & Roos 1990).

Since 1999, when a synopsis was presented for N.Z. species of Fissidens (Beever 1999), two major revisions of infrageneric classification of the genus have been published (Pursell & Bruggeman-Nannenga 2004; Suzuki & Iwatsuki 2007). Both revisions emphasised peristome teeth morphology, particularly of the filaments in the case of Suzuki & Iwatsuki. Information from costal structure, exothecial cells, axillary hyaline nodules, sexuality, and chromosome number was also utilised. Both classifications provided names for peristome types and for costa types, as well as for taxonomic groupings, with some names in common.

The classification of Pursell & Bruggeman-Nannenga (2004) is followed here (see synopsis below). It aligns more closely with that of the earlier N.Z. treatment by Beever (1999). The names of peristome types used in an earlier publication (Bruggeman-Nannenga & Berendsen 1990) are retained. Some significant features presented by Suzuki & Iwatsuki (2007) are considered in individual species treatments.

The subgeneric classification of genus Fissidens remains in a state of flux. Future molecular analysis, a technique yet to be applied systematically to this complex genus, could lead to a better resolution of natural groupings and their phylogenetic relationships.

In N.Z. 28 species are currently recognised, five of which are represented by two or more varieties.

In the key and descriptions that follow, unless otherwise stated, plant material is moist; leaf characters are for mid stem vegetative leaves; laminal cell dimensions are for dorsal laminal cells opposite the apex of the vaginant laminae and mid-way between the costa and the leaf margin; a "leaf border" (unless otherwise described) is composed of elongate, narrower, and often thicker-walled cells at the margin of a lamina; leaf border characters are for the dorsal laminal margin opposite the apex of the vaginant laminae; distinctions are not made between laminae (or borders) with two cell layers and those with three or more layers (both are referred to as "pluristratose"); and axillary hyaline nodules are mentioned only when they are well-developed.

The genus Fissidens is unique among mosses in its complex leaf morphology. Each leaf is composed of four laminae, with two vaginant laminae fused along the proximal part of the costa. These vaginant laminae together sheathe both the stem and (usually) also the basal part of the leaf above. Leaves are invariably attached to the stem in two ranks (distichously). The result is a shoot architecture that is sufficiently uniform to render the genus easily recognisable. Because of the complexity of the leaf and shoot architecture, specialised vocabulary has been developed to describe it. In this treatment, terms for this specialised architecture are as follows: each leaf consists of the two vaginant laminae, an apical lamina (distal to the vaginant laminae), and a dorsal lamina (occupying the whole of the leaf length on the opposite side of the costa). Vaginant laminae are said to be open (when the suture between them is confined to the costa), closed (when the suture extends from costa to leaf margin), or partially closed (when the suture extends part-way from costa to leaf margin); the vaginant lamina that is free (or partly free) at its apex is referred to as the "minor vaginant lamina". When minor vaginant laminae all lie on the dorsal face of the shoot in one rank of leaves, and on the ventral face in the other rank, the shoot is said to be "laterally heterostichous". The architecture of the Fissidens leaf is discussed and illustrated in detail by Beever et al. (2002).

A specialised terminology was developed by Bruggeman-Nannenga (1990) to describe variations in costal anatomy of Fissidens, as seen in cross-section, in the region of the vaginant laminae. These are defined for N.Z. material as follows:

bryoides-type: 2 lateral stereid bands, with 2 adaxial peripheral guide cells . F. anisophyllus, F. berteroi (modified bryoides-type), F. blechnoides, F. bryoides, F. curvatus, F. dietrichiae (modified bryoides-type), F. exilis, F. integerrimus, F. leptocladus, F. linearis, F. megalotis subsp. megalotis, F. perangustus, F. rigidulus, F. strictus, F. taylorii, F. tenellus, and F. waiensis.

oblongifolius-type: 3 bands of stereid cells (1 adaxial and 2 lateral). F. asplenioides (modified oblongifolius-type), F. capitatus, F. hyophilus, F. oblongifolius, and F. pallidus.

taxifolius-type: 2 lateral stereid bands, with 4 or more adaxial peripheral guide cells. F. adianthoides, F. crispulus var. robinsonii, F. dubius, and F. taxifolius.

Peristomes of Fissidens species have received such intensive study that special conventions have been developed for their description. The terminology used here largely follows that of Bruggeman-Nannenga & Berendsen (1990) and Pursell & Bruggeman-Nannenga (2004). Thus the terms "adaxial" and "abaxial" are employed here (as opposed to "inner" and "outer" elsewhere in this Flora) to designate peristome tooth surfaces. The term trabecula/e is used in a broad sense to apply to protruding horizontal anticlinal wall remnants on both adaxial and abaxial tooth surfaces (as opposed to such structures on the adaxial or "inner" surface only elsewhere in this Flora). The term lamella/e is used to describe cohering vertical walls between trabeculae on both adaxial and abaxial tooth surfaces (as opposed to protruding transverse wall remnants on the abaxial or "inner" surface elsewhere in this Flora). "Internal" features are those visible within the teeth using bright field light microscopy, but which are not seen with the SEM.

Six peristome types (of the nine types discussed by Bruggeman-Nannenga & Berendsen 1990) are found in N.Z. members of the genus. Their nomenclature follows Bruggeman-Nannenga & Berendsen (1990), with descriptions based on N.Z. material, as follows:

bryoides-type: teeth 30–72 µm wide at base, divided above into two strongly twisted (when dry) filaments; abaxial trabeculae of the undivided region of the tooth higher than lamellar ornamentation, the lamellae with horizontal papillose ridges; adaxial trabeculae of the undivided region of the tooth deep, variously ornamented; trabeculae usually not differentiated in distal region of the filament; filamental lamellae ornamented with oblique ribs, sometimes becoming horizontal towards the apex. F. anisophyllus, F. berteroi (modified bryoides-type), F. blechnoides, F. bryoides, F. curvatus, F. dietrichiae, F. leptocladus, F. perangustus, F. rigidulus, F. taylorii var. taylorii, F. taylorii var. epiphytus, and F. tenellus.

fasciculatus-type: teeth 65–100(–110) µm wide at base, divided above into two slightly twisted (when dry) and flattened filaments; abaxial trabeculae of the undivided region of the tooth higher than lamellar ornamentation, with lamellae pitted, the pits more or less in vertical and horizontal rows; adaxial trabeculae of the undivided region of the tooth shallow, coarsely papillose; trabeculae distinct in the filaments, except at extreme apex; filamental lamellae ornamented with papillae superimposed on vertical ribs. F. asplenioides.

sainsburia-type: teeth 50–70 µm wide at base, straight and more or less erect (wet or dry), undivided, rimose, or fenestrate, and thus anomalous within genus Fissidens; supra-basal abaxial trabeculae densely papillose, deeper than the papillose lamellar ornamentation, and with supra-basal adaxial trabeculae shallow, with densely papillose to reticulate lamellar ornamentation; distal trabeculae distinct with ornamentation finely papillose or irregular and obscure on distal lamellae. F. taylorii var. sainsburyanus.

scariosus-type: teeth 24–50(–60) µm wide at base, divided above into two strongly twisted (when dry) filaments; abaxial trabeculae of the undivided region of the tooth as high as lamellar ornamentation, the lamellar ornamentation consisting, on abaxial surface, of smooth horizontal ridges, with punctate ornamentation internally; adaxial trabeculae of the undivided region of the tooth deep, fimbriate or with coarse branched papillae; basal regions of filaments with abaxial trabeculae continuous with persistent vertical walls; distal regions of filaments with trabeculae indistinct, and lamellae with oblique ribs. F. dealbatus, F. exilis, F. hylogenes, F. integerrimus, F. linearis.

similiretis-type: teeth 52–90 µm wide at base, divided above into two twisted (when dry) filaments; abaxial trabeculae of the undivided region of the tooth as high as lamellar ornamentation, or somewhat emergent, the ornamentation consisting, on the abaxial surface, of smooth horizontal ridges, with punctate ornamentation internally; adaxial trabeculae of the undivided region of the tooth deep, trabeculae and lamellae there usually ornamented with columnar papillae, but occasionally smooth; basal regions of filaments with abaxial lamellae ornamented with closely spaced vertical striae; distal regions of filaments with trabeculae weakly differentiated, and lamellae ornamented with deflexed squamae. F. capitatus, F. hyophilus, F. oblongifolius, and F. pallidus (modified similiretis-type).

taxifolius-type: teeth 80–130 µm wide at base, divided above into two slightly twisted (when dry) filaments; abaxial trabeculae of the undivided region of the tooth higher than lamellar ornamentation, with lamellae pitted, the pits more or less in vertical and horizontal rows; adaxial trabeculae of the undivided region of the tooth shallow, ornamented with short-columnar papillae; trabeculae distinct throughout the filament, and filamental lamellae ornamented with oblique ribs. F. adianthoides

For seven taxa, peristomes from N.Z. material have been unavailable for study: for F. waiensis and F. rigidulus var. pseudostrictus (taxa endemic to N.Z.) capsules are unknown; for F. crispulus var. robinsonii, F. megalotis subps. megalotis, F. dubius, and F. taxifolius capsules are unknown in N.Z.; and for F. strictus only immature capsules are known in N.Z.

In Fissidens, leaves on a given shoot differ in morphology, depending on the developmental stage of the shoot apex when they were initiated: juvenile (sensu Mishler 1988), vegetative, and sexually reproductive. Juvenile leaves are produced as initial leaves developing from a vegetative bud on a protonema or rhizoid, or at the base of an innovative shoot on an existing shoot system. At maturity the first formed juvenile leaves are small and scale-like, and may consist of a costa and vaginant laminae alone. As the ontogenetic sequence continues, dorsal and apical laminae of successive leaves are gradually larger; if borders are a feature they may also be increasingly well-developed. Mishler (1988) has argued persuasively that the morphology of first-formed juvenile leaves supports the hypothesis that the dorsal and apical laminae of the Fissidens leaf were phylogenetically derived as outgrowths from the apex and costa of a typical moss leaf.

Perichaetial and perigonial leaves are usually specialised in form in Fissidens, and their vaginant laminae are often fully open, regardless of the configuration in vegetative leaves. In addition, the vaginant laminae of perichaetial and perigonial leaves are usually broader in relation to the rest of the leaf, thus accommodating the enclosed gametangia. Typically perigonial leaves have an emarginate apex on the vaginant laminae, forming a conspicuous shoulder.

Many species are quite variable (Pursell, 1994; 2007), particularly with respect to the extent and robustness of their leaf borders; this variability adds to the difficulty of their circumscription.

In terms of their ecology in N.Z. Fissidens species are terricolous, saxicolous, or, in a few cases, epiphytic; many are primary colonisers of bare earth. Natural sites of disturbed soil, such as at the base of wind-thrown trees and on eroding stream banks, are now greatly augmented by cut trackside and roadside banks. These may bear swards of Fissidens square metres in extent. Oligotrophic freshwater environments frequently support several species of Fissidens. Within N.Z., records of the genus are mainly from below 1000 m elevation, reflecting its predominantly tropical distribution. Only two species, F. adianthoides and F. rigidulus, routinely extend above the tree-line.

Fissidens ceylonensis Dozy & Molk. is a predominantly tropical species, with Australian records from northern Western Australia, the Northern Territory and in far-north-eastern Queensland (Stone & Catcheside 2012). It has been recorded for N.Z. (Wijk et al. 1962; Gangulee 1969–1972, pp. 512, 514; Iwatsuki & Suzuki 1988). However, no N.Z. specimens have been located. It is probable that the record of Wijk et al. (1962) in Index Muscorum (from which the later N.Z. records may have been derived) stems from geographic confusion: F. bicolor Thwaites & Mitt. was listed as "aus Neu-Irland" by Müller (1900), and was then placed in synonymy of F. ceylonensis by Fleischer (1904).

Fissidens linearis var. obscurirete (Broth. & Paris) I.G. Stone is recorded from tropical Asia, Japan, New Caledonia and Queensland, Australia. Study of the holotype of var. obscurirete shows that it differs from N.Z. material of F. linearis in the percurrent to shortly excurrent costa, the costa not obscured by papillose lamina cells, and in the well-developed border on the margin of the vaginant laminae of perichaetial, vegetative, and even of some juvenile leaves. Stone (1990a, p. 241) commented that "Rarely plants… [of F. linearis var. linearis] which verge towards the var. obscurirete have been found in New Zealand (e.g. in J.E. Beever 35-15)". The variety is not accepted for N.Z.

Fissidens zollingeri Mont. is a widespread species, known from tropical and subtropical Asia, Oceania, and Australia (Northern Territory, Queensland and north-eastern N.S.W.). It was noted by Dixon (1923, p. 107) as possibly occurring in N.Z., based on "a few stems…among some plants of F. inclinabilis received from Mr D. Petrie collected near Dunedin". The plants were producing "numerous large, green, elongate, jointed propagula among the leaf-axils". Fissidens zollingeri is similar to F. curvatus, but differs in having axillary propagula, conspicuous axillary hyaline nodules, costa ± straight at apex of vaginant laminae, a synoicous inflorescence, erect capsules, and a scariosus-type peristome (I.G. Stone, pers. comm., Oct. 1992). The Petrie specimen could not be located, and additional N.Z. material has not been seen. Considering the tropical and subtropical range of the species the Dunedin record seems unlikely, and this species is not considered further.

The status of Fissidens tenellus var. leptochaete (Dusén) J.E.Beever & I.G.Stone is discussed under F. tenellus.