Arthonia epiramboldia M.Westb., Isaksson & Frisch, 2025

Westberg, Martin, Isaksson, Robin & Frisch, Andreas, 2025, Two new lichenicolous Arthonia species from Scandinavia, Phytotaxa 682 (1), pp. 68-80 : 73

Arthonia epiramboldia M.Westb., Isaksson & Frisch , sp. nov. ( Fig. 2 b,c , 3 a,b )

MycoBank No: MB853108

Diagnosis: New lichenicolous Arthonia (affiliated to the Bryostigma clade) on Ramboldia cinnabarina ; characterized by non-aggregated, black ascomata, sessile on the host thallus, 0.11 ± 0.03 mm diam.; epithecium and hypothecium olive brown to dark red-brown, K+ olive green, without distinct apical caps on the paraphysoids; ascospores hyaline, slipper-shaped, 1-septate with a slight constriction at the septum, 9–13 × 4–5.5 µm; hymenial gels I+ vinose, KI+ sky blue.

Type:— Sweden. Jämtland: Frostviken par., Storvallbäcken, 500 m NW of Blåsjösätern, 64.85051°N 14.07317°E, elev. 498 m, on Ramboldia cinnabarina on Salix , 28 July 2022, R. Isaksson, R. Vicente & M. Svensson (UPS L-1050778, holotype).

Etymology: The new taxon is named after its host, Ramboldia cinnabarina .

DNA barcode sequences: PP541611, PP541612.

Description: Lichenicolous fungus, infection causing a pale brownish discolouration of the host thallus including soralia; vegetative hyphae were observed in the host thallus near the ascomata, c. 3–4 µm wide, thick-walled (0.5–1.0 µm), I+ vinose, KI+ pale blue. Ascomata scattered or in small colonies, not aggregated but often concentrated on the soralia of the host, superficial, rounded, flat to slightly convex, black, emarginate, 0.06–0.18(–0.22) mm diam. (n=76, average 0.11 ± 0.03 mm), in section 80–110 µm tall. Proper exciple c. 10 µm wide. Epithecium c. 10 µm tall, olive brown to dark red-brown. Hymenium colourless, 40–50 µm tall. Hypothecium dark brown to reddish brown. Paraphysoids loosely branched and netted, c. 1–1.5 µm wide, extending laterally above the asci, tips to 3 µm wide, sometimes with a thin dark brown cap. Asci Arthonia - type, broadly clavate, 25–36 × 14–19 µm (n=11), 8-spored. Ascospores slipper-shaped, hyaline, 1-septate, (9.0–)10.8 ±0.9(–13.0) × (4.0–)4.6 ±0.4(–5.5) µm (n=72), slightly constricted at the septum, with a smooth perispore, c. 1 µm wide, browning of over-aged spores not observed. Pycnidia not seen.

Chemistry: Host thallus not tested; ascomatal gels I+ vinose, KI+ sky blue. A tiny I+/KI+ blue ring structure in the tholus in the asci. Ascospores I/KI–, but with a I+ pale vinose, KI+ pale blue perispore. Dark brown ascomatal pigments turn olive green in K.

Ecology and Distribution: Arthonia epiramboldia parasitizes the thallus of Ramboldia cinnabarina often sitting on the soralia of the host. The known specimens were collected on Alnus incana , Betula sp. , Picea abies , and Salix caprea in boreal forests or subalpine birch forests in northern Sweden from Jämtland to Torne lappmark. In addition, two specimens from Finnmark in northern Norway were discovered in herbaria UPS and O, probably collected from Juniperus communis . All host thalli seen were fertile and appear to be healthy apart from a pale brownish discoloration of the thallus in the infected areas.

Notes: Arthonia epiramboldia is the first lichenicolous Arthonia described from Ramboldia Kantvilas & Elix (1994: 296) ( Ramboldiaceae ). The species is phylogenetically closely related to A. protoparmeliae and A. toensbergii ( Fig. 1 ). Apart from the host selection, A. protoparmeliae differs by larger (up to 0.35 mm diam. and up to 140 µm tall), glossy black apothecia that are often densely aggregated to confluent on the apothecial disc of its host ( Thor et al. 2023: Fig. 9), darker pigmentation in epi- and hypothecium, and larger, more elongated ascospores, 12–16(–20) × 4–5(–6) µm ( Etayo 2010, Thor et al. 2023). According to current knowledge, A. protoparmeliae is a species of exposed low alpine to alpine heathlands with rich to calcareous bedrock and known from the Pyrenees in northern Spain, the Shetland Islands, and Fennoscandia ( Etayo 2010, Hitch 2015, Thor et al. 2023). From A. toensbergii , A. epiramboldia differs by reddish brown rather than olive brown apothecial pigments and slightly shorter, more broadly rounded ascospores. Arthonia toensbergii is restricted to Mycoblastus affinis ( Schaerer 1850: 132) Schauer (in Poelt & Steiner 1964: 230) and M. alpinus ( Fries 1831: 335) Hellbom (1884: 102) . It is currently only known from highly oceanic or otherwise humid spruce forests in Norway, and is here reported new to Sweden from two localities (see below) in western Jämtland and western Åsele lappmark, respectively.

Additional specimens examined: Norway. Finnmark: Alta, Alten, Bosekop, 1 July 1864, Th. M. Fries (UPS L-789831, filed under Ramboldia cinnabarina ); Porsanger/Karasjok, inter Skovanvarre et Gourmikloubal, s.d., J.M. Norman s.n. (O-L-104321, filed under Ramboldia cinnabarina ). Sweden. Jämtland: Frostviken par., Lerdalsälven, 64.73413°N 13.9322°E, on Ramboldia cinnabarina on Alnus incana , 20 Aug. 2020, F. Larsson (UPS L-985760); Frostviken par., 1.6 km WNW of Stora Blåsjön, Storvallbäcken, 64.84926°N 14.06896°E, elev. 475 m, on Ramboldia cinnabarina on Alnus incana , 20 Sept. 2023, R. Isaksson & K. Soler Kinnerbäck (UPS L-1095118); Rätan par., c. 8 km SSW Klaxåsen, forest S Brännan, c. 800 m SSW Kvinnfolksbaracken, 62.3°N 14.37°E, elev. 615 m, 20 Sept. 1991, M. Wedin 3927 (UPS L-019041, filed under Ramboldia cinnabarina ). Lule lappmark : Jokkmokk par., Karats area, E of Berghem, Luvosluspen, 66.64668°N 18.81106°N, elev. 420 m, open coniferous forest, on the soralia of Ramboldia cinnabarina on the base of Picea abies , 23 July 2021, M. Westberg SCNB128 (UPS L-1049446). Torne lappmark : Karesuando par., Ainvarpiojokka, near Naimakka, 18 July 1910, B. Lynge (UPS L-789828, filed under Ramboldia cinnabarina ).

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.