Arthonia scrobiculatae Frisch & M.Westb., 2025

Westberg, Martin, Isaksson, Robin & Frisch, Andreas, 2025, Two new lichenicolous Arthonia species from Scandinavia, Phytotaxa 682 (1), pp. 68-80 : 74-77

Arthonia scrobiculatae Frisch & M.Westb. , sp. nov. ( Fig. 2 a , 3 c–g )

MycoBank No: MB853109

Diagnosis. New lichenicolous Arthonia (affiliated to the Bryostigma clade) on soralia of Lobaria scrobiculata ; characterized by the adnate, non-aggregated, matt, (brownish-) black ascomata not visibly breaking through the host thallus, 0.1–0.25 µm diam.; medium olive-brown epi- and hypothecium with distinct apical caps on the tips of the paraphysoids; hyaline, slipper-shaped, 1-septate ascospores with slight constriction at the septum, 13–20 × 4–6.5 µm; hymenial gels I+ vinose, KI+ sky blue; and a KI+ blue ring in the tholus.

Type.— Norway, Troms. Bardu, Berglund , 68°49′06.4′′N 18°32′59.7′′E, on a large Sorbus aucuparia in boreal deciduous forest, elev. 170 m, 18 July 2019, A. Frisch 19/No5 (O-L-243326, holotype; O-L-243327, isotype) .

Etymology. The new taxon is named after its host, Lobaria scrobiculata .

DNA barcode sequences: PP541605, PP541606.

Description: Infection not causing discolouration of the host thallus; c. 2–3 µm wide, thick-walled (0.5–1.0 µm) vegetative hyphae, I+ vinose, KI+ pale blue, were observed in the host thallus near the ascomata. Ascomata in small colonies of up to 20, not aggregated, irregularly rounded to short elliptical, adnate, moderately convex, not visibly breaking through the host thallus, (brownish-)black, matt, emarginate, minutely scabrid-verruculose, 0.1–0.25 mm diam., in section 60–80 µm tall. Proper exciple 15–20 µm wide, medium olive-brown, darker towards the outer edge due to dark olive-brown pigment plaques and caps on the hyphal walls, of more compacted paraphysoidal hyphae. Epithecium 7–10 µm tall, olive-brown. Hymenium hyaline, 40–60 µm tall. Hypothecium up to 20 µm tall, pale to medium olive-brown. Paraphysoids loosely branched and netted, c. 1.5–2.0 µm wide, embedded in dense gelatinous matrix; tips upright to slightly horizontally extending above the asci, widened to 2.5–4.0 µm, with distinct dark olive-brown caps. Asci Arthonia - type, broadly clavate, with thin lateral walls (c. 1–1.5 µm), 35–45 × 15–18 µm (n=10), 8-spored (spores in 2–3 irregular rows), with broadly triangular ocular chamber. Ascospores slipper-shaped, hyaline, 1-septate, (13.0–)15.8 ±1.6(–20.0) × (4.0–)5.7 ±0.5(–6.5) µm (n=35), constricted at the septum, with thin wall and septum (≤0.5 µm), with narrow, smooth perispore (≤0.5 µm); browning of over-aged ascospores not observed. Pycnidia not seen.

Chemistry: Host thallus not tested; ascomatal gels I dil +, I+ vinose, KI+ sky blue. A tiny I+/KI+ blue ring structure in the tholus observed in the asci. Ascospores I/KI–, but with a I+ pale vinose, KI+ pale blue perispore. Olive-brown ascomatal pigments unchanged or slightly more greenish in K.

Ecology and distribution: Arthonia scrobiculatae grows on the soralia of Lobaria scrobiculata . The species is known from Nordland and Troms in Norway and from Lule lappmark and Torne lappmark in Sweden. It was collected in Norway from large Sorbus aucuparia and Salix caprea trees in oceanic, birch dominated boreal deciduous forests. In Sweden it was collected from an exposed boulder in a low alpine habitat.

Notes: Arthonia scrobiculatae is phylogenetically closely related to A. circinata ( Fig. 1 ). That species forms distinct necrotic infections on the thallus of various Umbilicaria Hoffman (1789: 8) species and the apothecia are aggregated in the center of the infection or formed in a distinct circular arrangement. The internal ascoma organisation of both species is similar, but the ascospores of A. circinata are smaller than in A. scrobiculatae , 10.5–14 × 4–6 µm (n=15), and the apothecial pigments are reddish brown rather than olive-brown. Unlike Grube et al. (1995), we observed a tiny KI+ blue ring-structure in the tholus of the asci of A. circinata . Orange-red, K+ purple granular crystals in the hymenium that are reported for possibly old infections of A circinata ( Grube et al. 1995) are lacking in A. scrobiculatae .

A few lichenicolous Arthonia species have been described from Lobaria species in the tropics, including A. subconveniens Nylander (1867: 440) , A. ricasoliae Müller Argoviensis (1887: 424) , and A. lobariellae Etayo (2017: 91) ( Etayo 2017, Wedin & Hafellner 1998). Based on the detailed descriptions in the cited literature, none of these species are similar to A. scrobiculatae , nor do they seem to be related to the Bryostigma clade. Taxa with apothecia similar to the new species have been described from southern Argentina and Chile from Pseudocyphellaria Vainio (1890: 182) ( Lobariaceae ) species ( Wedin & Hafellner 1998): A. subaggregata Wedin & Hafellner (1998: 84) differs from A. scrobiculatae by aggregated to confluent apothecia, 0.08–0.2 mm diam., an unpigmented to pale brownish hypothecium, paraphysoids lacking apical caps, and smaller ascospores, 8–10.5 × 3.5–4.5 µm. This species is known from Pseudocyphellaria hirsuta ( Montagne 1835: 88) Malme (1899: 18) and P. dubia Du Rietz (1926: 2) in Tierra del Fuego, Argentina, and from southern Chile. Arthonia minuta Wedin & Hafellner (1998: 75 , nom. illegit.; not Arthonia minuta Vainio 1915: 178 ) differs by much smaller, 0.07–0.1 mm, dark brown apothecia, tips of the paraphysoids being periclinally arranged in the epithecium, lacking apical caps, and smaller ascospores, 9.5–14 × 4–4.5 µm. This species is known from Pseudocyphellaria coriifolia ( Müller Argoviensis 1883: 55) Malme (1889: 25) in Tierra del Fuego, southern Argentina. It has been doubtfully synonymized with Bryostigma muscigenum (Etayo & Sancho 2008) . Arthonia santessoniana Wedin & Hafellner (1998: 81) differs by tips of the paraphysoids being periclinally arranged in the epithecium, lacking apical caps, and smaller ascospores, 11–14 × 4.5–6 µm. This species is known from Pseudocyphellaria scabrosa Santesson (in Galloway 1986: 155) and Pseudocyphellaria spp. in Tierra del Fuego, southern Argentina, and from New Zealand.

Additional specimens examined: Norway. Nordland: Beiarn, Bjørnstad N, 67°0′8.5′′N 14°27′14.5′′E, on Salix caprea in tall herb birch forest, elev. 205 m, 20 July 2021, A. Frisch 21/No1659 (O-L-243328). Troms: Bardu, Berglund, 68°49′06.4′′N 18°32′59.7′′E, on a large Sorbus aucuparia in birch dominated boreal deciduous forest, elev. 170 m, 18 July 2019, A. Frisch 19/No25 (TRH L-23827); ibid., 68°48′58.1′′N 18°33′22.4′′E, on a large Salix caprea in birch dominated boreal deciduous forest, elev. 200 m. 18 July 2019, A. Frisch 19/No26 (TRH L-23828); Storfjord, Langbakkan, 69°17′11.4″N 20°27′53.5″E, in boreal deciduous forest, elev. 195 m, 5 Aug. 2022, J.T. Klepsland JK383 (TRH L-43911). Sweden. Lule lappmark : Jokkmokk par., Padjelanta National Park, c. 10, 6 km E of Arasluokta, N of Mt Snålttje and S of the river Miellädno, 67.38976°N 17.04213°E, elev. 747 m, on the soralia of Lobaria scobiculata on a large, exposed boulder in alpine area, 10 Aug. 2022, M. Westberg PAD443 (UPS L-1073200); ibid. 67.39137°N 17.04086°E, elev. 735 m, 10 Aug. 2022, U. Arup L22182 (LD). Torne lappmark : Jukkasjärvi par., Vuoskoåive, 20 Aug. 1943, J. Eriksson (UPS L-051674, filed under Lobaria scrobuculata ).

Additional specimens examined for comparison with other species: Arthonia circinata : Norway. Oppland: Lom, Galdbygdi, 61.72025°N 8.34932°E, elev. 600 m, on Umbillicaria vellea , 31 July 2019, J.T. Klepsland JK 19-322 (O-L-226233). Finnmark: Alta, N slope of Komsa (Kongshavnfjellet), 69°59′12′′N 23°16′46″E, 87 m, on Umbilicaria vellea , 26 July 2015, A. Frisch 15/No53, 54 (TRH L-652391); ibid., Bosekop, 1864, Th.M. Fries s.n. (O-L-171817); ibid., in Alten ad Kongshavenfjeld, s.d., J.M. Norman s.n. (O-L-171815, 171816, 171818). Arthonia epipolytropa : Norway. Troms: Kåfjord, Kåfjorddalen, Guolášjávri: W of Goddejávri, 69.35249°N 20.87972°E, elev. 916 m, on Lecanora polytropa , 13 Aug. 2022, A. Frisch 22/No778 (TRH L-34598). Arthonia protoparmeliae : Norway. Oppland: Dovre, Grimsdalen, NW of Grimsdalshytta, 62.0926°N 9.6286°E, on Protoparmelia badia , 5 July 2011, H. Holien 13165 (TRH L-14537, filed sub Rhizocarpon geographicum ). Nordland: Bodø, Skjevlfjellet N, 67.01167°N 15.12833°E, elev. 685 m, on Protoparmelia badia , 14 July 2021, J.T. Klepsland 21/No1722 (TRH L-24957). Finnmark: Varanger Peninsula, Båtsfjord, Båtsfjorddalen, near the exit to Syltefjord, 70.58°N 29.66°E, elev. 82 m, 2 July 2014, M. Westberg VAR062 (S). Arthonia toensbergii : Norway. SØr-TrØndelag: Meldal, along river Svorka, 63.1344°N 09.8231°E, elev. c. 220 m, on Mycoblastus affinis , 16 Oct. 1992, H. Holien 5482 (TRH L-1848); Rissa, Storlidalen along river Nordelva, 63°40′09.9′′N 09°58′03.9′′E, elev. 170–185 m, on Mycoblastus affinis , 27 Sept. 2017, A. Frisch 17/131 (TRH L-17890); Åfjord, Høydalmoan nature reserve, 64°02′29.0′′N 10°26′38.0′′E, elev., 100–130 m, on Mycoblastus affinis , 21 July 2017, A.Frisch 17/133 (TRH L-17891); Osen, Seterelva nature reserve, 64°13′24.4′′N 10°40′36.2′′E, elev. 110–130 m, on Mycoblastus affinis , 13 July 2017, A. Frisch N4-2-Pa4-1 (TRH L-17893). Troms: Bardu, Berglund, 68°49′06.4′′N 18°32′59.7′′E, elev. 160–175 m, on Mycoblastus alpinus , 18 July 2019, A. Frisch N15-2-Bp1-2 (TRH L-23959). Sweden. Jämtland: Frostviken par., Pluttbäcken, ca. 400 m NNW of Långviken, 64.70193°N, 13.91014°E, on Mycoblastus on Picea , 18 Sept. 2023, R. Isaksson & K. Soler Kinnerbäck (UPS L-1104323); Åsele lappmark : Vilhelmina par., Saxnäs, Krokbäcken, 64°57′44.2′′N 15°20′7.6′′E, 555 m, on Mycoblastus affinis , 14 Aug. 2023, A. Frisch 23/Se9 (O-L-243330); ibid., Saxnäs, Handsktummen, 64°45′23.3′′N 14°12′39.2′′E, 515 m, on Mycoblastus affinis , 14 Aug. 2023, A. Frisch 23/Se14 (O-L-243331).

Figures

FIGURE 1. ML phylogenetic tree of the Bryostigma clade in Arthoniaceae. Arthonia epiramboldia and A. scrobiculatae are in larger boldfaced font. Bayesian (first) and ML bootstrap (second) support is indicated for each node. Opegrapha vulgata (Opegraphaceae) is the operational outgroup.

FIGURE 2. Habitus images. a) Arthonia scrobiculatae (O-L-243326, holotype), b) Arthonia epiramboldia (UPS L-789831), c) Arthonia epiramboldia (O-L-104321); Scales: a = 0.5 mm, b, c =1 mm.

FIGURE 3. a, b) Arthonia epiramboldia (UPS L-1050778, holotype):a) section of apothecium, b) ascospores.c–g) Arthonia scrobiculatae (O-L-243326, holotype): c) section of apothecium, d) hymenium with ascus and ascospores in water, e) ascospores in water, f) ascospores in KI, g) hymenium with ascus and ascospores in KI; note the hemiamyloid ring structure in the tholus of the ascus. Scales: a, c = 50 µm, b, e, f = 10 µm, d, g = 20 µm.