Orthotrichum dentatum T.Kiebacher & Lüth, 2016

Thomas Kiebacher & Michael Lüth, 2016, Orthotrichum dentatum T. Kiebacher & Lüth sp. nov. (Orthotrichaceae), Journal of Bryology 38, pp. 1-11 : 1-9

Orthotrichum dentatum T.Kiebacher & Lüth sp. nov ( Figures 1–5 )

Type: Italy: Trentino - Alto Adige , South Tyrol , Feldthurns , Tschiffnon , 46°40 ′ 26.1 ′′ N, 11°36 ′ 18.6 ′′ E, 874 m a.s.l., in a garden on bark at the stem of a solitary Juglans regia tree, 0 1 August 2014, T. Kiebacher 650 (holotype: BOZ: Bryo 1188 ; isotypes: MAUAM: Brio 4840 , priv. herb. T. Kiebacher).

Paratypes: see Appendix 1.

Diagnosis: Orthotrichum dentatum is similar to Orthotrichum schimperi Hammar but differs from it in the presence of denticulate to dentate leaf apices, a distinctively hairy calyptra, strongly keeled leaves and exostome teeth that are light orange to pale or light brownish coloured.

Description: Plants 0.2 – 0.7 (– 1.1) cm tall, in (moderately dense –) dense and compact cushions up to 1.5 cm in diameter, (blackish-green –) dark green to occasionally yellowish-green, light brown to brown at base. Rhizoids reddish-brown to brown, 10 – 25 μm in diameter, smooth, sparse to very dense at base, lacking or scattered above. Stems branched, sub-pentagonal in transverse section, with a 1 – 3 layered sclerodermis of thick-walled brownish cells; pith cells enlarged, hyaline to light brownish, thin walled, in the transition zone to the sclerodermis with corner thickenings; central strand absent. Axillary hairs up to four per leaf axil, filiform, composed of 2 – 8 (– 9) rectangular, hyaline cells, the 1 (– 2) lowermost cells narrower, shorter and light brown.

Leaves erect and appressed to slightly flexuous when dry, sometimes curved towards the axis giving the shoots a knobby julaceous appearance; especially in upper and perichaetial leaves, the uppermost portions of the leaves frequently pointed towards the axis; when wet, leaf base more or less erect, and upper 2 / 3 – 4 / 5 of the lamina patent to spreading to slightly recurved in some lower leaves.

Upper leaves 1.8 – 2.6 × 0.45 – 0.8 (– 0.9) mm, lanceolate to ovate lanceolate, broadest in lower half, attached in an arched, v-shaped or more or less straight line, not decurrent or short and narrowly decurrent, slightly concave, strongly keeled in the upper half; when dry, the two sides of the lamina typically spread at an angle of ± 60° but spread is limited to 30° (– 20°) in some leaves; when wet, keel slightly less pronounced but spreading angle in most upper leaves <90°; margins recurved to revolute, from base or from above base almost to apex, in the upper half of the leaf frequently broadly revolute and thereby narrowing the lamina; from the end of the recurved margins leaf lamina more or less abruptly tapering to a triangular, acute (– acuminate) and frequently apiculate apex; apex flat to keeled, sometimes channelled or cucullate; apiculus of 1 – 3 (– 5) quadrate to rectangular green or hyaline cells, sometimes bent, s-shaped or reflexed, especially in leaves in the apical part of young, not yet fruiting shoots; leaf margins entire below, at apex irregularly papillose-crenulate to denticulate and dentate, sometimes coarsely so, rarely completely entire. Costa strong throughout, at 1 / 3 of leaf length from base 40 – 64 (– 70) μm wide, at extreme base up to 100 μm wide, sometimes slightly widened in the uppermost part, ending in the apex, on dorsal face covered by mostly isodiametric laminal cells from above base to apex; ventrally with two rows of elongate cells (usually with thick and weakly wavy longitudinal walls). Basal leaf cells mainly rectangular, (10 –) 1 1 – 25 × (15 –) 2 0 – 80 (– 87) μm light green, almost hyaline at extreme base, gradually becoming darker moving upwards, occasionally groups of hyaline cells adjacent to the rib; walls thin or slightly incrassate with nodose cell walls present in at least some leaves; pits not observed; marginal cells shortly rectangular to quadrate, frequently with strong transversal walls and pronounced corner thickenings; cells gradually becoming shorter and smaller upwards. Upper leaf cells mostly isodiametric, (9.5 –) 1 2 – 20 (– 25) μm wide; quadrate, penta- or hexagonal; walls incrassate with pronounced corner thickenings; lumina subangular to rounded or ellipsoid; leaf cells papillose, except at base, on ventral and dorsal face with (1 –) 2 (– 3) simple, blunt, rather low (up to as high as wide) papillae, the papillae are generally placed on the proximal and distal part of the cell, often forming longitudinal lines on the leaf surface. Lamina unistratose, in upper and perichaetial leaves occasionally with short bistratose rows or small cell groups.

Lower leaves usually gradually smaller, more narrowly lanceolate to almost lingulate, less sharply keeled and more gradually tapering to a sharp, triangular apex with a generally long and frequently whitish apiculus.

Gemmae sometimes present but usually sparse, formed on leaf margins as well as on the ventral lamina and dorsally on the costa, especially on lower leaves, consisting of up to 10 or sometimes more cells, simple or branched.

Cladautoicos or gonioautoicous. Perichaetial leaves similar in shape and gradually differentiated from the upper leaves, with a markedly wider base and the margins in the lower part of the lamina plane or only slightly recurved, broadly ovate lanceolate, strongly constricted in the upper third, up to 2.7 × 1.2 mm. Vaginula 0.15 – 0.3 (– 0.35) mm long, shortly cylindrical to truncated conical, naked. Ochrea at base cylindrical to (slightly) conic, widened above, enclosing the base of the capsule, fringed, reaching half way up the neck. Calyptra 1.4 – 1.9 × 0.7 – 1.13 mm, conic when young, conic-oblong to oblong-conic when mature, sometimes slightly constricted at base, gradually or abruptly tapering to a conical tip; straw coloured, paler towards base and gradually brownish above, very rarely with inconspicuous longitudinal brownish or orange tinged stripes, tip chestnut to dark brown coloured; with 10 – 17 prominent longitudinal ridges, between the ridges with strong plicae or almost plane when mature, sparsely to densely hairy with 10 – 60 uneven sized hairs arising from the ridges; hairs concentrated in the upper part of the calyptra but absent on the tip, lacking or sparse at base, from very short and thornshaped to 0.65 (– 0.8) mm long, rarely shortly overtopping the tip, straw coloured or sometimes whitish, mostly thick and robust, from uniseriate to 3 (– 5) -seriate, at base also polyseriate, more or less curved and flexuous, sparsely to moderately papillose with predominately low papillae (rarely higher than wide), located mainly on the transversal walls and at the tips; surface and ridges of the calyptra not papillose but occasionally with slightly protruding transversal cell walls on the ridges.

Seta 0.17 – 0.4 (– 0.5) mm long, sometimes widened in the upper part.

Capsule immersed to half emergent, urceolate when dry, markedly to moderately constricted below mouth, abruptly or gradually narrowing to the seta, dark brown, gradually light brown to very pale towards the base; when wet, barrel shaped to champagne glass shaped, abruptly or rather gradually narrowing into the seta; strongly ribbed when dry; ribs very prominent, often touching each other and thereby covering the furrows, almost reaching the base or vanishing in the lower third of the capsule, sometimes continued as plicae spirally twisting to the seta. Urn 0.85 – 1.15 mm long, neck 0.3 – 0.5 mm long, neck / urn ratio ranging between (0.27) 0.32 and 0.59. Exothecial cells of the furrows pale, thin walled; cells of the ribs strongly differentiated, light brown, enlarged, with strongly thickened longitudinal walls and less thickened transversal walls, above usually in four rows, further down subdivided into up to nine rows, vanishing in the lower third of the capsule. Stomata 7 – 14 per capsule, immersed, variably arranged around the middle of the capsule, occasionally individual stomata also in the upper or lower third of the capsule; from almost uncovered by scarcely differentiated exothetical cells to completely covered by strongly protruding, thick-walled cells; usually more strongly covered in the lower part of the capsule. Lid moderately convex to almost flat, ca 0.4 mm in diameter with an outer ring of 2 – 3 (– 4) rows of orange to light-red cells; beak straight, blunt, smaller than the width of the lid.

Prostome occasionally present, discontinuous, 1 – 3 cells high, papillose. Peristome double. Exostome of eight pairs of teeth, teeth (160 –) 180 – 225 (– 250) μm long, triangular; sometimes, especially when old, partially splitting, slightly fenestrated at top or lacunose along the division line; recurved and closely appressed to the exothecium when dry, light orange at sporulation, thereafter light brown to pale, contrasting with the colour of the exothecium; external side of teeth (outer peristome layer, OPL) densely papillose with blunt papillae on reticulate structures and on very scarce to more or less abundant vermicular ridges (visible as striae under a light microscope) that are generally transversally arranged in lower fields, radially arranged in median fields and longitudinally arranged in upper fields; internal side of teeth (exostome primary peristome layer, PPL) smooth throughout or towards the apex with scattered low papillae. Endostome of eight segments 130 – 180 μm long, 0.64 – 0.83 times as long as the exostome teeth, erectincurved to strongly incurved when dry, variable in shape, from slender, linear and uniseriate with hardly thickened transversal walls to stout, subulate, asymmetrically biseriate with oblique, strongly thickened walls; gradually or abruptly widened to a more or less broad base; hyaline to very light yellowish or pale brownish; external side of segments (endostome PPL) smooth, internal side of segments (inner peristome layer, IPL) smooth or occasionally very finely sculptured; connective membrane low, frequently fragmented. Spores 12 – 18 (– 20) μm, olive-green with brownish walls, coarsely papillose.

Taxonomy: Orthotrichum dentatum fits into the subgenus Pulchella (Schimp.) Vitt , section Diaphana Vent. in Husn. , as described in Lewinsky (1993).

Etymology: The specific epithet dentatum is derived from the characteristically dentate leaf apices of the new species. Dentate leaf apices are rather uncommon within the genus Orthotrichum , and they separate the new species from similar species.

Ecology and Habitat: The localities of the new species are characterized by a temperate montane climate with sub-Mediterranean influences at its southernmost localities. High temperatures, however, seem to be unfavourable for the species. So far O. dentatum has not been found at warmer, lower altitude sites in the southern Alps. The species has been found between 528 and 1340 m a.s.l. Orthotrichum dentatum prefers open, well-lit to slightly shaded environments; it has never been found inside closed forest stands. The species grows as an epiphyte on the stems and branches of deciduous trees and seems to perform especially well on Juglans regia and Tilia L. sp. The bark of these tree species is characterized by high nutrient content, low acidity and a high buffer capacity ( Barkman, 1958). In addition to Juglans regia and Tilia sp., so far O. dentatum has been recorded on Acer platanoides L., A. pseudoplatanus L., Aesculus hippocastaneum L., Betula pendula Roth. , Celtis australis L., Fraxinus excelsior L., F. ornus L., Prunus armeniaca L., P. avium (L.) L., P. cerasus L., P. domestica L., Salix L. sp., Sorbus aucuparia L. and Ulmus glabra Huds.

The most frequent co-occurring species with Orthotrichum dentatum is O. schimperi and the two species often intermix. Orthotrichum dentatum is also very frequently associated with O. diaphanum Brid. , Nyholmiella obtusifolia (Brid.) Holmen & E.Warncke and Syntrichia papillosa (Wilson) Jur. Less frequently associated species include Orthotrichum affine Brid. , O. anomalum Hedw. , O. pallens Brid. , O. pumilum Sw. ex anon., O. rogeri Brid. , O. scanicum Grönvall , O. speciosum Nees and O. striatum Hedw.

Distribution: So far, O. dentatum has been found in the Alpine range in northern Italy and eastern Switzerland ( Figure 6 ). In Italy, the species has been recorded at several sites in the province of South Tyrol. In Switzerland, it has been recorded in the cantons of Ticino and Appenzell Ausserrhoden.

Discussion

Orthotrichum dentatum is most similar to O. schimperi . The two species are both very small and are similar in habit. Both species have immersed to slightly emergent, urceolate, strongly ribbed capsules with a short neck that usually tapers abruptly to the short seta. However, the two species differ in a set of characteristics that allows one to unmistakably separate plants belonging to either one of the two species (Table 1). Orthotrichum dentatum differs most from O. schimperi by its dentate leaf apices, strongly keeled leaves and the hairy calyptra. Some irregular teeth may rarely also occur on leaf apices of O. schimperi , but they are by far less pronounced than in O. dentatum . The denticulation of the leaf apices in O. dentatum is variable; single leaves can be entire but in all examined plants some leaves with conspicuously dentate leaf apices were found. The calyptra of O. schimperi rarely has short scattered hairs and in some cases in O. dentatum the papillose calyptra hairs might be few, but the two species also differ in the shape and colour of the calyptra. In O. schimperi , the calyptra is short, hemispherical to bell-shaped, whitish or yellowish, and it usually has conspicuous orange or brownish longitudinal stripes. In O. dentatum , the calyptra is more elongated, vividly straw coloured and only very rarely has inconspicuous longitudinal stripes. In O. dentatum , the leaves, especially the upper ones, are strongly keeled in their upper part. The two sides of the lamina usually spread in an angle which varies around 60°, whereas in O. schimperi this angle is rarely lower than 90°. Less obvious differences in the morphology of the leaves are the comparably rare occurrence of bistratose stripes in the upper lamina and the generally more acute leaf apices in O. dentatum . Furthermore, in O. dentatum , the uppermost and perichaetial leaves are usually constricted in their upper part due to unevenly recurved leaf margins. Thus they usually become narrower in a convex line compared with a more or less straight to concave line in O. schimperi . The differences in the sporophytes of the two species are subtle and gradual. On average, in O. dentatum the capsule becomes narrower more gradually towards the seta compared with O. schimperi . Furthermore, in O. dentatum the stomata are usually arranged around the middle of the capsule, and at least some stomata are usually more than half covered by strongly differentiated exothetical cells. In O. schimperi , the stomata usually are above the middle of the capsule and most are only slightly covered by the exothetical cells. The ornamentation of the OPL can be very similar in the two species, although vermicular ridges are often expressed in O. dentatum and are lacking or very scarce in O. schimperi . The appendices of the inner peristome of O. dentatum tend to be less stout than in O. schimperi . In the latter, they are usually irregularly biseriate with strongly thickened oblique walls and they have a pronounced, broad base. In O. dentatum , the segments of the endostome are variably uni- to biseriate with variably thickened walls and the broad base is usually less pronounced.

When using determination keys for Europe ( Lewinsky-Haapasaari, 1995; Lara et al., 2009), O. dentatum might be mistaken for O. philibertii due to the similarly hairy calyptra. The most striking differences between the two species are the shape of the leaf apex and the calyptra. In O. philibertii , the leaf apex is more or less abruptly narrowed to a distinctive, more or less triangular, and usually entire acumen. The calyptra of O. philibertii is usually less elongate and the calyptra hairs are more robust, frequently 2 – 3-seriate above, less curved and more densely papillose than in O. dentatum . Furthermore, in O. philibertii the calyptra is whitish to yellowish whereas in O. dentatum it is straw coloured. The sporophytes of the two species are similar but in O. philibertii the segments of the inner peristome are usually uniseriate with only slightly thickened walls and are thus more fragile.

Another minute Orthotrichum species where dentate leaf apices are occasionally present, and which might be mistaken for O. dentatum , is O. pumilum Sw. ex anon. However, as with O. schimperi , the dentation of the apices is never as pronounced in O. pumilum as it is in O. dentatum . Furthermore, O. pumilum differs from O. dentatum in the capsules: in O. pumilum , capsules are only slightly constricted below the mouth and have a longer capsule neck which usually narrows gradually towards the seta. In addition, O. pumilum has less strongly keeled leaves and has linear, usually uniseriate endostome segments, which are as long or almost as long as the exostome teeth and have hardly thickened transversal walls.

Further European Orthotrichum species where denticulations of the leaves occur and that share the small size and immersed to emergent capsules are O. diaphanum Brid. and O. vittii F.Lara, Garilleti & Mazimpaka. These two species differ from O. dentatum in that they have hyaline leaf apices formed by elongate cells. Other minute European Orthotrichum species are O. microcarpum De Not. , which differs in that it has plane leaf margins, and O. macrocephalum F.Lara, Garilleti & Mazimpaka , which differs in that it has broadly rounded leaves.

Orthotrichum tenellum Brid. and O. scanicum share the occasionally dentate leaf apices and the hairy calyptra with O. dentatum . They differ from O. dentatum in their larger size (both are usually around 1 cm high) and in their usually distinctly longer seta (Table 1). Furthermore, O. scanicum differs from O. dentatum in having 16 endostome segments and in the exothetical bands which are only 2 (– 3) cells wide.

The characteristically dentate leaf apices of the new species led us to name it O. dentatum . Dentate leaf apices are a rather rare characteristic within the genus Orthotrichum . Most species have entire leaves ( Lewinsky, 1993). Apart from the species mentioned above, denticulations occur in O. denticulatum Lewinsky (known from Africa), O. bartramii Williams (North- and Central America), O. rivulare Turner (Europe and North America) and O. spiculatum F.Lara, Garilleti & Mazimpaka (South America).

The numerous descriptions of new Orthotrichum species within the last three decades indicate that Orthotrichum is a genus which has not been studied extensively enough in former times. Nevertheless, it is surprising that such a distinctive species as O. dentatum has previously been overlooked in a well-studied area (see Mari, 1894; Limpricht, 1895; Culmann, 1915; Mönkemeyer, 1927; Jäggli, 1933, 1950; Düll, 1991; Cortini Pedrotti & Lara, 2001).

Figures

Figure 1 Orthotrichum dentatum T. Kiebacher & Lüth in southern Switzerland. (A) Lime tree (Tilia sp.) where O. dentatum was found for the first time in Switzerland. (B) Orthotrichum dentatum together with O. schimperi Hammar on the bark of the lime tree. The tuft in the front right position is O. dentatum and the tuft in the back left position is O. schimperi.

Figure 2 Dry tuft of Orthotrichum dentatum T. Kiebacher & Lüth with the characteristic straw coloured, hairy calyptrae and strongly ribbed capsules with reflexed, pale exostome teeth. M. Lüth 8009.

Figure 3 Orthotrichum dentatum T. Kiebacher & Lüth. (A) Habit, dry. (B) Shoot, wet. (C) Stem section. (D. 1) Median, (D. 2) upper and (D. 3) perichaetial leaves. (E) Decurrent leaf base of (E. 1) median and (E. 2) upper leaf. (F) Axillary hairs. (G) Leaf apices of (G. 1) upper leaves, (G. 2) leaves from a male branch with long apiculi. (H) Basal leaf cells. (I) Basal marginal leaf cells. (J) Upper leaf cells. (K) Leaf apex with gemmae formation. (L) Gemmae. (M) Calyptra. (N) Calyptra hairs. (O) Capsule, wet and dry. (P. 1) Upper, (P. 2) median, and (P. 3) lower stoma. (Q) Uppermost part of capsule with exothetical cells, base of exostome teeth and prostome remains. (R) Peristome, internal view. (S) Endostome segments. Scales: (A, B, D, M, O) 500 μm; (C, E, F, G, K, L, N) 100 μm; (P, Q, R, S) 50 μm; (H, I, J) 20 μm. (A – F, G. 1, H – K, O – R, S. 1) From holotype; (G. 2, L) T. Kiebacher 716; (M, N) T. Kiebacher 782; (S. 2) T. Kiebacher 986.

Figure 4 Morphological diagnostic characters of Orthotrichum dentatum T. Kiebacher & Lüth. (A) T. Kiebacher 705; (B) T. Kiebacher 704; (C) T. Kiebacher 782; (D) T. Kiebacher 711; (E) T. Kiebacher 716.

Figure 5 Scanning electron microscopy images of Orthotrichum dentatum T. Kiebacher & Lüth. (A) Shoot with capsule. (B) Shoot with calyptra. (C) Capsule mouth and peristome. (D) Prostome remains (indicated by the arrows). (E) Smooth surface of the primary peristome layer (PPL) of an exostome pair of teeth. (F) Endostome segment with smooth PPL. (G) Endostome segment with smooth inner peristome layer (IPL). (H) Ornamentation of the outer peristome layer (OPL) of an exostome pair of teeth. (I) Detail of the basal exostome OPL with papillae on transversal ridges. (J) Detail of the ornamentation of the median and apical exostome OPL with longitudinal, transversal, and radial ridges. (A – F) From holotype; (G – J) T. Kiebacher 675.

Figure 6 Known distribution of Orthotrichum dentatum T. Kiebacher & Lüth in the Italian and Swiss Alps. The localities are cited in Appendices 1 and 2. USGS EROS Data Center; ESRI: ArcWorld Supplement and Data Solutions, B. V.