Arthonia buelliae Zhurb., 2021

Zhurbenko, Mikhail P., 2021, Arthonia buelliae sp. nov. (Arthoniaceae, Arthoniales, Ascomycota) and other noteworthy lichenicolous fungi from the Primorye Territory of Russia, Phytotaxa 483 (2), pp. 183-189 : 184

Arthonia buelliae Zhurb. , spec. nov. ( FIGURE 1 )

MycoBank number: 838496

Diagnosis:—Lichenicolous ascomycete growing on Buellia . Similar to Arthonia sampaianae but hymenium hyaline, ascospores shorter, 15–24 × 6–9 µm vs. 20–26 × 6–8 µm, rarely submuriform, and growing on Buellia vs. Nevesia .

Type :— RUSSIA. Primorye Territory : Bay of Peter the Great of the Sea of Japan, Rikord Island, elev. 10 m, 42°52’06.4”N, 131°39’34.5”E, open coastal siliceous rocks, on Buellia stellulata (thallus), 15 September 2013, M.P. Zhurbenko 13177 ( LE 310171— holotype!) .

Ascomata apothecia, immersed in galls, with ±flat, blackish, slightly glossy, epruinose, irregularly circular, angular, oblong or linear discs 50–250 µm in length, located at the gall surface level, without proper margin, but occasionally surrounded by slightly elevated host tissues, cupulate in cross-section with a concave or flat bottom, 100–180 µm tall, sometimes contiguous, aggregated up to 50 or more on a gall. Galls semi-globose, up to 1.5 mm diam., composed of host thallus with healthy-looking photobiont cells, but also here and there including clearly delimited aggregations of brown prosoplectenchymatic hyphae, sometimes developing under the ascomata like a stalk. Exciple rather indistinct, subhyaline, 10–15 µm thick, in cross-section composed of 3–5 layers of circular or tangentially elongated cells 3–7 µm in length, with walls 1–2 µm thick. Hymenium hyaline, 80–170 µm tall (including epihymenium), with widely spaced asci, I+ blue then reddish-brown, K/I+ blue with occasional reddish patches. Epihymenium conspicuous, brown, K+ greyish brown, 10–25 µm tall. Subhymenium hyaline, rather indistinct. Paraphysoids branched and anastomosed, frequently septate, 1–2 µm thick; apical cells brown, without dark caps, often enlarged to 2.5–5 µm thick, non-granulose. Asci broadly clavate, with thickened apical cap, without a ring-structure visible in K/I, 55–85 × 16–25 µm, 8-spored, I−, K/I−. Ascospores initially hyaline, smooth, occasionally with a halo up to 1 µm thick, soon becoming light brown to brown (K+ greyish brown) and granulate due to a distinct perispore, non-halonate, septa much darker coloured, obovoid with slightly wider upper cell, sometimes oblong or ellipsoid, the apices rounded to somewhat attenuated, (15.4–)16.5–20.3(–23.8) × (6.2–)7.1–8.5(–9.3) µm, L/W = (1.2–)2.0–2.6(–2.8) (n = 47), with (1–)2–3 trans-septa, very rarely submuriform, with an additional longitudinal septum in the central segment, sometimes slightly constricted at the septa, irregularly 1–2(–4)-seriate in the ascus.

Distribution and host:—The new species is known only from the type collection in Russian Asia growing on the thallus of saxicolous Buellia stellulata . It induces distinct galls on the host thallus, otherwise not visibly damaging the host.

Etymology:—Growing on Buellia .

Notes:— Arthonia buelliae differs from most species of the genus in the absence of a K/I+ blue ring in the ascus apex, phragmo- to exceptionally dictyosporous ascospores and gall induction ( Grube 2007). In many respects, it resembles Arthonia sampaianae (Diederich & Etayo) Ertz & Diederich growing on Nevesia sampaiana , a gallinducing species with 3-septate, eventually brown ascospores (Ertz et al. 2005). However, the latter species can be distinguished by a brownish hymenium and longer ascospores, 20–26 × 6–8 µm, which are never submuriform. Arthonia plectocarpoides (S.Y.Kondr. & D.J.Galloway) Wedin & S.Y.Kondr. growing on Pseudocyphellaria and A. tremelloides Etayo growing on Heterodermia induces similar galls, which, at least in the latter species, also include brown prosoplectenchymatic hyphae ( Wedin & Hafellner 1998, Etayo 2002). Nonetheless, both species are quite distinct by their 1-septate ascospores. According to Diederich et al. (2018) 93% of the known lichenicolous Arthonia species are confined to one genus of lichens; none of them previously was reported on Buellia . In its gall induction, immersed ascomata interspersed with sporadic aggregations of brown prosoplectenchymatic hyphae, and trans-septate, brown, granulate ascospores Arthonia buelliae recalls some species of Plectocarpon Fée , but the latter readily differ in having stromatic ascomata and more slender asci with an apical K/I+ blue ring.

Figures

FIGURE 1. Arthonia buelliae (holotype).A, ascomata immersed in galls on the thallus of Buellia stellulata. B, ascoma and gall with an aggregation of brown prosoplectenchymatic hyphae in cross-section in water. C, ascoma in cross-section in water. D, ascoma in crosssection in I; note I+ blue then reddish-brown reaction. E, epihymenium in water (on the left) and K (on the right). F, paraphysoids in K. G, asci in K/I. H, ascospores in water (on the left) and K/I (on the right); note immature hyaline ascospores (at the top right). Scales: A = 0.5 mm, B–D = 50 μm, E–H = 10 μm.