Taxonomic treatment of the family Polytrichaceae Schwägr . in Sri Lanka

This article is published under the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract: Sri Lanka harbors a rich diversity of mosses (Phylum Bryophyta) with 561 species, 185 genera and 55 families. According to the checklist of mosses of Sri Lanka by O’Shea (2002), Polytrichaceae Schwägr. represents one of the most species-rich families comprising of two genera (Atrichum and Pogonatum) with 12 species. Available details on species and genera of the family are limited to mere literature based lists; no taxonomic keys, descriptions or monographs for therecorded species are available. The present study was carried out to investigate the species diversity and prepare a taxonomic treatment of the Family Polytrichaceae in Sri Lanka. Polytrichaceae is unique among other moss families by the formation of an epiphragm from the columella, presence of photosynthetic lamellae on upper leaf surface and multicellular peristome appearing single with 32 to 64 teeth. Specimens were collected from all possible geographic localities including; NuwaraEliya, Thispane, Horton Plains, Adam’s Peak, Piduruthalagala, Badulla, Kanneliya Rain Forest, Riverston, Deanston, Corbert’s Gap, Deraniyagla, Elkaduwa, Gannoruwa, Mahakanda, Loolecondera, Kurunegala, Jaffna, Anuradhapura, Dambulla and Galle. Specimens were thoroughly examined for morphological and anatomical characters using, dissecting and light microscopes and identified up to specific/ generic level using taxonomic keys, descriptions and monographs. The specimens collected during the study represented two genera (Atrichum and Pogonatum) genera and seven species of the family Polytrichaceae in Sri Lanka: Atrichum crispulum Schimp. Ex Besch., Pogonatum aloides (Hedw.) P. Beauv., P. marginatum Mitt., P. microstomum (Schwägr.) Brid., P. neesii(C. Müll.) Dozy, P. subtortile (C. Müll.) Jaeg. and P.urnigerum (Hedw.) P. Beauv. A taxonomic key to Sri Lankan Polytrichaceae and descriptions along with illustrations for all the species identified are presented. Further investigations are made to explore all recorded species by O’Shea (2002) and to trace their distribution patterns within the island.

Sri Lanka is a tropical island with a high diversity of bryophytes, and harbours 327 liverworts, 561 mosses and 07 hornworts species (Abeywickrama and Jansen, 1978a;Abeywickrama and Jansen, 1978b;Abeywickrama and Jansen, 1960;Long and Rubasinghe, 2014;Mitten, 1859;O'Shea, 2002;O'Shea, 2003;Ruklani et al., 2016;Tixier, 1975;Tixier, 1983).Taxonomic studies on Sri Lankan bryophytes initiated only recently and therefore, apart from the lists of taxa, taxonomic descriptions, identification keys, phenological data or details of distribution patterns remain poorly understood.Scarcity of taxonomic information is one of the main barriers to carry out any research on this important group of plants within the country.The study presents the first specimen based taxonomic treatment of the family Polytricaceae Schwäger in Sri Lanka.
According to the checklist of mosses by O'Shea (2002), the family Polytrichaceae represents one of the most species rich moss families in Sri Lanka with two genera and 12 species (Table 1).However, the recorded number of taxa is primarily based on literature-based checklist published by O'Shea (2002) with only a few specimens deposited at the National Herbarium Peradeniya.The present study was carried out to investigate the species diversity and prepare a taxonomic treatment of the family in Sri Lanka.

Microscopic methods
Specimens were rehydrated prior to observations.Specimens were observed under dissecting (Hertel & Reus-Optik Kassel), and light microscopes (Eruomex, Arnhem, Holland).Morphological and anatomical characters were observed and characters were recorded for each specimen studied.

Taxonomic keys and descriptions
A taxonomic key for the family Polytrichaceae in Sri Lanka was prepared using unique characters of the species identified.Taxonomic descriptions were prepared for each species identified using their gametophytic and sporophytic characters observed.

Herbarium specimens
Herbarium specimens were prepared following Schofield (1985) method.Voucher specimens are deposited at National Herbarium Peradeniya (PDA).

RESULTS AND DISCUSSION
According to the checklist of mosses by O'Shea (2002), two genera (Atrichum and Pogonatum) and 12 species of the family Polytrichaceae are recorded from Sri Lanka (Table 1 Plants small, medium to occasionally tall or large, intufts or forming colonies.Stems erect, acrocarpous, rigid, arising from persistent protonemal mats or from subterranean rhizomes that grow on siliceous or acidic substrata, usually unbranched; stem in cross section with distinct central conducting strand composed of hydroids (hydrome) and leptoids (leptome) (Figure 1A).Leaves spirally arranged, lower leaves small, often scale-like and appressed to the stem,upper leaves (limbs), often crowded, long and narrow, differentiated into a broad, pale, unistratose, membranous, sheathing base (Figure 1C) and a firm blade; lamina margin 1(3) stratose, entire to distinctly serrate, or with specialized elongated marginal cells; costa single, prominent, narrow at sheathing part, usually broad and percurrent to slightly excurrent; whole or parts of the upper leaf surface covered with numerous, longitudinal, ribbon-like photosynthetic lamellae (Figure 1B).Lamina cells isodiametric; sheath cells mostly rectangular to linear, narrower towards the margin (Eddy, 1988;Hyvönen, 2012;Ignatov, 1995).
Plants usually found on siliceous sandy or loamy soils in exposed habitats or earth covered rocks in damp, sometimes wet and more rarely on dry habitats (Nyholm, 1971).Distributed in temperate regions, Europe, Asia, U.S.A., North Africa and Australia (Lou and Koponen, 1986).
Note: Atrichum crispulumis distinguished by its broad leaves with few, short lamellae, long narrow, curved capsules.The species mostly prefers shady, wet environments, often wet banks along streams (Hyvönen, 2012;Stoneburner et al., 1992).Ceylon Journal of Science 48 (1) 2019:3-17 Distribution: The species is also known from North America, China and Japan.
Plants variable in height, with rosette-like species forming compact mats or loose lumps (~ 8 mm), and robust speciesreaching 20 cm (Eddy, 1988),with or without conspicuous persistent protonema.Stem erect, simple or branched, lower part of stem loosely or densely covered or not covered with rhizoids.Stem anatomy mostly similar among species, consisting of epidermis, cortex and central conducting strand; epidermis mostly unistratose with brownish, thick walled, closely arranged cells; cortex multilayered, with large, loosely arranged, hyaline, parenchyma cells; stereides present in central cylinder and beneath epidermis, thick walled and closely arranged, stereides beneath epidermis reddish or yellowish, stereides in central cylinder hyaline or reddish, leptoides present surrounding central cylinder, with tightly arranged, thin walled, hyaline parenchyma cells.Leaves spirally arranged or in rows, green or whitish green, erect and spreading when moist, dark green or brownish when dry, lanceolate; costa percurrent or excurrent, usually broad and shallow, often toothed on abaxial side towards leaf apex.Leaf margin dentate, rarelyentire, unistratose or occasionally bistratose.Photosynthetic lamellae usually well developed, covering most of the leaf surface, occasionally few confined to costa, 2-7 cells high, crest cell smooth or papillose, round, flat or slightly notched or cone shaped.

Note:
The short rosette-like, stiff, dark green plants with triangular leaves resembling small Aloe plants is characteristic of the species.The species is closely related to P. nanam (European species) and are difficult to distinguish without sporophytes (Hyövonen, 1989).According to Hyövonen (1989), plants of P. aloides are larger, and have distinct marginal serrations along the entire blade and costa has numerous teeth.Also, leaf apices of P. nanum are wide and rounded whereas those of P. aloides are acute (Hyövonen, 1989).
Distribution: The species is also known from Europe, New Zealand, Asia and Africa (Hyövonen, 1989).Plants 25-38 mm tall, pale to dark green, delicate, forming compact mats, persistent protonema absent.Stem reddish, erect, unbranched, diameter 0.4-0.7 mm;basal part covered with small, greenish scale leaves; rhizoids brownish, absent or present only at base of stem.Leaves arranged in three rows, two lateral rows and one ventral row, ventral leaves smaller than lateral leaves, bright green, erect, spreading when moist, dark green, strongly incurved, altered and not appressed whendry, lanceolate,5-6 mm long, apex acute with a hyaline leaf tip, apical base wide, leaf shoulders and sheath not developed, extended leaf base present, 0.9-2.0mm long; cells of extended leaf base reddish brown, elongated, rectangular, thick-walled, chloroplasts absent or 3-4; costa percurrent, prominent on both surfaces; costa cells light greenish, long rectangular, thin-walled, chloroplasts 12-19; teeth on abaxial surface of costa absent or up to 2 towards apex, hyaline, sharp, 02 cells high; leaf margin, dentate from apex to middle, entire towards leaf base, with 2-7 cells; marginal teeth one layered, 3-5 cells high; marginal tooth cellsthick-walled, green, mostly spherical to irregular, chloroplasts 3-5, crest cell often larger and translucent.Lamina cells on upper surface of leaf loosely arranged without rows, thin-walled, mostly spherical, light greenish and entire, on lower surface loosely arranged, mostly spherical to irregular, mostly isodiametric, thin-walled, hyaline, chloroplasts 6-10; lamina cells at leaf base long rectangular, not isodiametric, hyaline, chloroplasts 4-5.Teeth absent from leaf lamina.Leaf lamina except at costa unistratose.Photosynthetic lamellae not developed.Thick-walled 8-11, greenish cells found along costa.
Distribution: The species is also known from India and Vietnam (Daniels et al., 2016).
Plants 25-60 mm tall, green, forming robust loose mats, persistent protonema absent.Stem erect, unbranched, reddish,diameter 0.4-0.6mm,basal part densely covered with hyaline to brownish rhizoids and small, brownish scale leaves.Leaves spirally arranged, upper surface olive to dark green, lower surface slightly brownish green or slightly brown, erect and spreading when moist, reddish brown, slightly incurved, slightly altered and appressed when dry, lower leaves dark green or reddish brown, shorter than upper leaves or same as upper leaves, broad lanceolate, 5-9 mmx1.0-1.2mm,apex acute with a brownish or reddish tip, apical base wide, leaf shoulders and sheath well developed, shoulder margin dentate, sheath slightly yellowish brown, margin entire, extended leaf base absent; costa percurrent, slightly prominent on lower surface or not, not prominent on upper surface, dark brown; costa cells light brown, rectangular, thick-walled, reddish brown at sheath, 17.5-52μmx10.5-21.0μm; chloroplasts absent or 2-4; teeth on abaxial side of costa 17-42, brown, sharp, 1-3 cells high; leaf margins unistratose, 2-3 marginal cells; marginal cells thin-walled, usually hyaline to slightly yellow, short rectangular, chlorophyllose, dentate from apex to shoulders, marginal teeth 01 row; marginal teeth cells in upper half and lower half of leaf similar, 1-3 cells high, sharp, thick walled, dark reddish brown, chloroplasts absent.Leaf lamina multistratose with 2-3 layers, lamina cells on upper surface closely arranged into continuous rows, thin-walled, cone shaped, entire, on lower surface from apex to base loosely arranged, mostly rectangular, thick walled, chlorophyllose, teeth absent from leaf lamina.Sheath cells thin-walled at apex and middle, thick-walled at base, short rectangular at apex and middle, long rectangular at base, hyaline, chlorophyllose.Photosynthetic lamellae 49-74,well developed, 3-4 cells high,densely arranged throughout the leaf surface except atmargin, erect; lamellae  Note: This species can beeasily identified in the field by its robust habit, apically wide and basally narrow leaf blade, olive to brownish leaves.Double bottle-shaped apical cells of lamellae are diagnostic of the species.
Plants dioicous.Sporophyte terminal.Seta reddish, reddish brown or brownish, single, unbranched, erect, 10-34 mm long.Capsule long cylindrical, erect or slightly inclined, mostly symmetrical, 3-4 mm long, without lid, greenish, smooth when fresh, dark green, ridged when dry, exothecial cells mamillose; epiphragm brown to slightly yellowish, light gray or white; peristome teeth 32, reddish, pink or brownish, elongated triangular, 0.1-0.2mm.Calyptra light brown, completely hairy.Spores greenish yellow, spherical, margin entire, diameter 7-10μm.Note: Pogonatum neesii is the most common species of Polytrichaceae in Sri Lanka with a wide geographical range (162 m-2230 m).The species has been collected from various localities during the present study.This species is characterizedby its long (4-7 cells) photosynthetic lamellae with notched, slightly larger, finely papillose crest cells and pale leaf margins of dry plants which are easily seen with a hand lens.Pogonatumneesii is closely related to P. aloides.However, the apical cells P. aloides are mostly rounded in cross section whereas those of P. neesii are typically retuse (Hyvönen, 1989).

Note:
The species can be distinguished by the presence of wide leaves, lamellae with 2-3 cells, round apical cells similar to lamellae cells.
Distribution: The species is also known from Indonesia, Malaysia, Papua New Guinea, Philippines, Fiji, Samoa and Solomons (Hyvönen, 1989).
Plants 50-75 mm tall, robust, glaucous green, forming dense mats, persistent protonema absent.Stem reddish, erect, unbranched, most part of the stem free from leaves, diameter 0.4-0.5 mm, basal part densely or loosely covered with hyaline or brownish rhizoidsand green to brownish scale leaves.Leaves spirally arranged, whitish green, erect, spreading when moist, dark green or yellowish brown, slightly incurved, altered, appressed when dry, whitish green on both surfaces, lower leaves whitish green or brown,shorter than upper leaves, narrow lanceolate, 5-7 mm long, apex acute with yellowish orange or yellowish brown tip, apical base narrow, shoulders and sheath well developed, shoulder margin entire, sheath hyaline, sheath margin entire, extended leaf base absent; costa percurrent or not, not prominent on any surface, costa cells green or light brownish, hyaline or reddish brown at sheath, rectangular, thin or thick-walled, 14-42 μm x7-14 μm, chlorophyllose; teeth on abaxial side of costa 7-25 brown, sharp, 1-3 cells high; leaf margin unistratose, dentate from apex to middle, entire towards base, marginal cells clearly visible, 3-5, thin walled, hyaline, mostly spherical or irregular, chlorophyllose or not, marginal teeth 01 row, 1-3 cells high, marginal teeth cells sharp, thick or thin-walled, yellowish or hyaline at upper half and hyaline at lower half, devoid of chloroplasts or with few.Leaf lamina multitratose with 2-3 layers, lamina cells on upper surface closely arranged into continuous rows, thin-walled, spherical, papillose or entire, on lower surface mostly spherical or mostly irregular to spherical at apex, mostly spherical at middle and base, loosely arranged, mostly isodiametric, 7-14 μm x 7.0-14 μm, thin-walled, greenish, chlorophyllose.Teeth absent from leaf lamina.Sheath cells thick or thin-walled, mostly spherical to irregular or short rectangular, hyaline, 7-38.5 μmx 10.5-17.5 μm.Photosynthetic lamellae 35-48, well developed, 5-7 cells high, densely arranged throughout leaf surface except at margin, erect, lamellae cells spherical, thin-walled, greenish, crest cell usually similar to lamellae cells or short rectangular, green, thin-walled, single celled, rounded, slightly notched or rectangular to spherical smooth or slightly papillose.

Note:
The species is characteristically robust and has distinct glaucous green colour.Pogonatum urnigerum is the most widespread species of the genus and is specifically variable in size, pattern of branching, leaf marginal dentations, form of crest cell (apical cell of lamellae) (Hyvönen, 1989).Sri Lankan specimens lack edexcurrent costa, strongly mammiloseexothecial cells, and coarsely papillose, thick-walled crest cells.However, according to Hyvönen (1989), these variations do not support segregation into sub-specific taxa.
Distribution: The species is also known from northern Eurasia, North America, Africa, south-east Asia and Papua New Guinea (Hyvönen, 1989).

CONCLUSIONS
The present taxonomic survey of Sri Lankan Polytrichaceae recognized one species of Atrichum (Atrichum crispulum  O'Shea (2002) were not reported during the present study.Further investigations are made with extensive field explorations throughout the country to locate all the species recorded, to study their phenology and to highlight the importance of conserving threatened taxa.

Figure 1 :
Figure 1: Vegetative characters of Polytrichaceae (A) transverse section of the stem of Pogonatum subtortile (B) transverse section of upper vegetative leaf of P. aloides (C) upper vegetative leaf of P. microstomum.

Figure 5 :
Figure 5: General morphology of Pogonatum (A) male gametophytes with perigonia on the top, (B) female gametophytes with the sporophytes (C) vegetative leaf blade with hyaline sheathing base (D) transverse section of stem (E) transverse section of leaf blade, (F) Hairy calyptra completely covering the capsule (G) capsule with lid, (H) epiphragm (I) part of transverse section of capsule wall, (J) spores.

Figure 7 :
Figure 7: Pogonatum marginatum Mitt.(A) female gametophytes with spporophytes, (B) dorsal surface of fresh habit (C) ventral surface of fresh habit (D) ventral leaf, (E) dorsal leaf (F) dry habit (G) transverse section of leaf at the nerve (H) transverse section at the leaf margin (I) leaf lamina cells, (J) transverse section of stem (K) calyptra covering the capsule, (L) dry capsule (M) spores.

Figure 8 :
Figure 8: Pogonatum microstomum (R. Br. ex Schwägr.)Brid.(A) fresh habit (B) dry habit (C) transverse section of leaf (D) vegetative leaf (E) leaf shoulder (F) teeth on back side of costa (G) leaf margin (H) leaf sheath cells (I) upper surface of leaf (J) lower surface of leaf (K) transverse section of leaf.

Figure 9 :
Figure 9: Pogonatum neesii (Müll.Hal.) Dozy (A) female gametophytes with sporophytes (B) transverse section of leaf with flat apical cells (C) transverse section of leaf with slightly notched apical cells (D) male gametophytes with perigonia (E) transverse section of leaf with flat, papillose apical cells (F) leaf margin (G) dry female gametophytes (H) part of transverse section of capsule wall (I) spores.