Pterygoneurum sampaianum (Guim.) Guim.

Hugonnot, Vincent, Kučera, Jan, Osman, Imen Ben, Daoud-Bouattour, Amina & Muller, Serge D., 2024, Pterygoneurum sampaianum (Guim.) Guim.: range extension to Africa, first mentions in France, confirmation of specific status and improved morphological circumscription, Cryptogamie, Bryologie 45 (4), pp. 37-48 : 43-46

Pterygoneurum sampaianum (Guim.) Guim.

EXAMINED SPECIMENS. — Tunisia • Tunisian Dorsal, Siliana Governorate, Delegation of Makthar, Sidi Ameur , site 2020-12; 35°52’47.46”N, 09°28’23.24”E; 710 m a.s.l.; 11.III.2020; leg. Ben Osman & Hugonnot; TUN2020-2 .

France • Pyrénées-Orientales , Opoul, Crest del Camp de l’Auca; 42°51’55.74”N, 02°54’1.22”E; 190 m; 6.III.2020; leg. Hugonnot • 42°51’49.52”N, 02°53’39.38”E • Aude , Fitou, Les Courtiels; 40°53’0.83”N, 02°57’41.28”E; 170 m; 6.III.2020; leg. Hugonnot • Savoie , Aussois , Maurienne valley, Barmettaz; 45°13’12.23”N, 06°44’49.82”E; 1300 m; 4.III.2021; leg. Hugonnot.

Spain • Torroella de Montgrí , L’Estartit , Cap Castell ; 42°4’44.5080”N, 03°11’41.1360”E; 12.II.2020; Vincent Hugonnot’s personal herbarium • Andalucía, Almería, Fondón, Sierra de Gádor, Barranco de Cacín ; 36°58’49.1”N, 02°48’46.7”W; c. 800 m; 28.IV.2015; leg. J. Kučera; CBFS 17331 , 17332 .

EMENDED DESCRIPTION

Previous morphological descriptions did not fully account for the morphological variability observed in the studied specimens whose identification was confirmed using molecular data. We therefore provide an emended morphological description of Pterygoneurum sampaianum .

Plants gregarious, in loose colonies characteristically consisting of very small sterile individuals and much larger fertile individuals, shortly bulbiform, whitish green to pale green, often with discolored tips, 1.25-1.8 (3.5) mm high. Axillary hairs 3-4 in axils of upper leaves, 9-12 ×100-130 µm, made of 1-2 basal cells short and 3-5 feebly colored and longer cells; terminal cell 9-10 ×30-35 µm. Subterranean part of stem thick and brown, 0.19-0.24× 0.45-0.55 mm, of thick-walled cells, with or without 1-2 non-chlorophyllous scales, proximally attached to substrate by 5-10 large brown rhizoids, 36-50 µm wide near base, often more than 6 mm long, ramified, strongly decreasing in size towards the apex (to 8 µm wide) and becoming hyaline, smooth but coated with fine soil material. Leafy stem aerial, unbranched or occasionally branched (often the smaller branch sterile, reduced to few leaves), with cortex undifferentiated (externally with smaller cells with barely thickened walls), central strand present but weak, of several cells. Proximal above-ground leaves reduced and hardly chlorophyllose, equally wide or wider than long, trapezoidal, suborbicular to rectangular, deeply concave, with none or very short acumen, awnless; basal marginal cells strongly differentiated into 2-4 cell-wide hyaline border, of long rectangular cells (5-7 ×40-50 µm), ascending along the margin; median and apical cells often very thick-walled. Distal leaves erect, deeply concave to convolute, awnless or with short straight hyaline smooth awn (70-100 µm long), individual leaves on some shoots occasionally bear a longer, up to 400 µm long, at times even flexuous hair, or many leaves piliferous on the same shoot; leaves wider than long, trapezoidal, 0.7-0.9× 0.7-0.8 mm, rarely longer than wide 0.4-0.5× 0.8-0.9 mm, widely rounded to truncate at apex, with plane margins; basal marginal cells forming a more or less distinct hyaline border, 3-6 cells wide, ascending to apical 1/3 of rectangular cells 10-14 × 40-70 µm, border totally missing at times; basal cells short-rectangular to quadrate, 15-22× 18-45 µm; median cells quadrate to rectangular, 8-15×8-20 µm; apical cells rounded quadrate to rounded rectangular, 7-13×8-18 µm, with thick walls, often hyaline; margin dentate from mid-leaf to apex, teeth formed by the protruding cells, often geminate. Costa 45-66 µm wide at base, adaxially expanded into 2-3 large lamellae to 15 cells high, running from base to apex, crenulated at margin by protruding conical cells (apex mamilla like, rarely with two mamilla-like ornamentations); terminal cells of lamellae 12-14×15-18 µm; surface of lamellae occasionally with short outgrowths of conical cells or small laminal outgrowths; cells of lamellae 14-20 ×18-30 µm; surface cells of costa thick-walled both abaxially and adaxially; abaxial walls of lamina cells more thickened than adaxial ones in transverse section, costa with 2-3 poorly differentiated guide cells, dorsal stereid layer not developed. Autoicous, male buds at stem base on ground level.

Sporophyte with red-brown urn. Seta 0.076 ×0.09× 1.4- 2.5 (3) mm, dextrorse; epidermal cells 8-13× 18-57 µm, with slightly thickened walls. Seta in transverse section with one layer of epidermal cell with outer tangentially thickened walls, central strand present. Urn shortly cylindrical, rarely cupulate, with faint longitudinal plicae when dry, wide-mouthed, 320-600 × 740-890 µm; exothecial cells irregularly rectangular, 18-32× 40-87 µm, with rather thin walls. Epidermal cell transverse section with tangentially not or very weakly thickened outer walls. Stomata 1-2, phaneroporous, at base of urn. Annulus poorly differentiated, of 1-2 rows of rectangular, barely vesiculose cells. Mouth with no trace of peristome (either at rim or in the operculum). Operculum with short and blunt beak, 0.40-0.65 mm long. Spores spherical, 35-58 µm across diameter, often ellipsoid or potato-shaped. Calyptra narrowly cylindrical at first, at maturity cucullate, rostrate, subobtuse at apex, covering urn at length (0.4-0.7 mm long).

HABITAT

Our observations allow us to identify the ecological requirements of Pterygoneurum sampaianum . The species is typically found in arid or semiarid climates. In the Maurienne valley of the French Alps, the locality is recognized as being among the driest in France, with an average annual rainfall of 518 mm / year, with the vegetation referred to as Festucetalia valesiacae Br.-Bl.&Tüxen ex Br.-Bl. 1949. The dominants include Festuca valesiaca Schleich. ex Gaudin , Stipa capillata L., S. eriocaulis Borbás , Euphorbia seguieriana subsp. loiseleurii (Rouy) P.Fourn. , Koeleria vallesiana (Honck.) Gaudin and Galium pusillum L. In the Isle-Crémieu, North Isère, France (Vénérieu, Simiaud and La Chanas; derelict marl quarry; 45°39’43”N, 05°17’17”W, 45°39’36”N, 05°17’17”W, 45°39’18”N, 5°16’33”W; 238 and 218 m a.s.l.; 3 March 2023; obs. S. Geoffroy, A. Labroche, Y. Longeot and M. Maglio) a calcareous plateau with an average annual rainfall much higher, of 950-970 mm / year, the vegetation where P. sampaianum have been spotted is a mosaic of mesoxerophilous grasslands of Tetragonolobo maritimi -Bromenion erecti J.-M.Royer 2006 and Teucrio montani -Bromenion erecti J.-M.Royer 2006 and thermophilous semi-wet meadows with Molinia caerulea (L.) Moench (Deschampsio mediae -Molinienion arundinaceae B.Foucault 2008) developed on outcrops of marl-limestone soil with temporary hydromorphy. In the eastern Pyrenees, the average annual rainfall is approximately 550 mm /year. The vegetation comprises degraded grasslands and garrigues with Brachypodium retusum (Pers.) P.Beauv. , Rosmarinus officinalis L., and is referred to the alliances Phlomido lychnitidis -Brachypodion retusi (Rivas-Martínez 1978) Mateo 1983 and Rosmarinion officinalis Br. -Bl. ex Molinier. In Tunisia, Pterygoneurum sampaianum was collected from the Tunisian Dorsal, which has an average annual rainfall of c. 400 mm /year. The plants were growing in low matorral vegetation composed primarily of solitary Pinus halepensis Mill. and Quercus ilex L. subsp. ballota (Desf.) Samp. , with Cistus clusii Dunal , C. creticus L., Rhamnus lycioides L. and Rosmarinus officinalis , belonging to the order Pistacio -Rhamnetalia alaterni Rivas-Martinez 1975 and the recently described alliance Loto dorycnium - Pinetum halepensis Djebaïli 2017 ( Meddour et al. 2017).

In the newly-discovered French populations, the species grows with rich assemblages of pioneer, mainly ruderal bryophytes, often belonging to the family Pottiaceae . In Savoy, the most frequently associated species are Aloina aloides (W.D.J.Koch ex Schultz) Kindb. , Bryum dichotomum Hedw. , Didymodon acutus (Brid.) K.Saito , Streblotrichum convolutum (Hedw.) P.Beauv and Tortula atrovirens (Sm.) Lindb. In Isère , main associated species are A. aloides , A. ambigua (Bruch & Schimp.) Limpr. , Microbryum curvicollum (Hedw.) R.H.Zander , Pottiopsis caespitosa (Brid.) Blockeel & A.J.E.Sm. , Ptychostomum imbricatulum (Müll.Hal.) Holyoak & N.Pedersen , Tortula caucasica Broth. , T. lindbergii Broth. and T. truncata (Hedw.) Mitt. In the Mediterranean localities they are Acaulon triquetrum (Spruce) Müll.Hal. , Aloina aloides , Bryum dichotomum , B. gemmilucens R.Wilczek & Demaret , Didymodon acutus , Microbryum curvicollum and M. davallianum (Sm.) R.H.Zander. Poorer communities are generally dominated by scarce individuals of only two species, Bryum dichotomum and Streblotrichum convolutum . In Tunisia, the species grows mostly without direct associates. In Andalucía, P. sampaianum grew in fissures of exposed conglomerate rock outcrops, and notable associated species included Aloina aloides , Campylostelium pitardii (Corb.) E.Maier , Crossidium aberrans Holz. & E.B.Bartram , Didymodon acutus (Brid.) K.Saito , D. desertorum (J.Froehl.) J.A.Jiménez & M.J.Cano , Encalypta vulgaris Hedw. , Entosthodon muhlenbergii (Turner) Fife, Pseudocrossidium revolutum (Brid.) R.H.Zander and Tortula atrovirens .

Most significantly, Pterygoneurum sampaianum generally occurs in very open micro-communities ( Fig. 4 ), with low cover of vegetation, and very sparse bryophytes, which strongly suggests a high sensitivity to competition. Although this is a generally well-known trait of Pottiaceae communities, the species’ apparent inability to invade more closed populations of larger species in the immediate vicinity appears to be significant. In the Pyrénées-Orientales and in Aude ( France), the species is strongly dependant on repeated trampling of paths in limestone plateaus where it grows in linear populations on a restricted fringe at the transition between small grassland communities and totally bare substrate (corresponding to car tracks or hiking paths).

The general association of Pterygoneurum sampaianum with fine clay and constraining substrates is also important. Initially it was believed to grow on the chalk clay of the Algarve ( Guimarães 1917) and on gypsiferous or saline soils in SE and NE Spain ( Guerra et al. 1995b). Casas & Brugués (1978) describe the microhabitat as a fine layer of clay deposited in the depressions. In Tunisia, the species is strongly linked to degraded habitats, mainly the flanks of small mountainous systems where fluvial flows during violent storms can carve rills and shape badlands characteristic of severely eroded soils. Important quantities of very fine-grained detritic “glacis” accumulate at the foot of the slopes, periodically regenerating new bare habitat suitable for the most diminutive Pottiaceae species.

An examination of the subterranean system of Pterygoneurum sampaianum , made of large and thick-walled rhizoids (compared to the significantly thinner rhizoids of P. ovatum ) anchored to semi-buried succulent stem, suggests that it could be linked to perennation. In the allegedly short-lived Acaulon triquetrum , long-term monitoring allowed Ahrens (2003) to uncover the species’ remarkable persistence which turns out to be pauciennial instead. This calls for further studies of similar small pottiaceous mosses since our knowledge of their biology is based on generalizations that do not seem to hold up with a careful individual examination.

CONSERVATION STATUS

The new data on Pterygoneurum sampaianum require to address the possible adjustments to its so far estimated conservation status. Based on the rare occurrences recorded so far in Europe, the species was evaluated as Near Threatened in the last version of European Red List of Mosses ( Sérgio & Cano 2019). This assessment has probably mainly been based on the situation in Spain where it is assessed as Least Concern ( Brugués & González-Mancebo 2012), as elsewhere in its distribution area, the species was evaluated as Regionally Extinct (RE) in Portugal and Data Deficient in Switzerland ( Hodgetts & Lockhart 2020). With the now more accurate morphological circumscription and better knowledge about its habitat in the Mediterranean region, additional records can be expected in the near future. However, vast areas of apparently favourable habitats that do not seem to be occupied by P. sampaianum exist in the Mediterranean. Considering the species’ apparent weakness in competition, ecological specialization, and apparent rarity, its threat status cannot currently be lowered but rather, it can be discussed to be evaluated as Vulnerable with respect to the population size which nearly certainly is smaller than 10 000 mature individuals and small individual populations hardly exceeding one hundred individuals in conjunction with the possibly decreasing overall size based on the suitable habitat degradation in the future risk assessment. Therefore, conservation efforts should focus on preserving the habitats where P. sampaianum occurs, ensuring the survival of this species for future generations.

Figures

FIG. 4. — Habitat of Pterygoneurum sampaianum (Guim.) Guim. (11 March 2020, Tunisia, Siliana Governorate, Sidi Ameur).