Linosporopsis ischnotheca (Desm.) Voglmayr & Beenken, comb. nov. Fig. 3.

MycoBank number: MB 833895; Index Fungorum number: IF 833895; Facesoffungi number: FoF;

Basionym. Sphaeria ischnotheca Desm., Annls Sci. Nat., Bot., sér. 3 18: 365. 1852.

Synonyms. Linospora faginea Sacc., Michelia 1(no. 4): 405. 1878. Linospora ischnotheca (Desm.) Sacc., Syll. fung. (Abellini) 2: 356. 1883.

Pseudostromata immersed in dead overwintered leaves, forming a distinct black clypeus (107–)145–247(–315) μm wide (n = 88) on both sides of the leaf, consisting of a textura epidermoidea-intricata composed of thick-walled, dark brown, septate hyphae 1.5–3 μm wide in dead host epidermis cells. Ascomata perithecial, scattered, solitary, immersed in dead leaf tissue, globose to ellipsoid, 230–340 μm diam., with a distinct central apical papilla 100–145(–160) μm wide at the base. Peridium (19–)22–32(–38) μm wide (n = 23), hyaline, pseudoparenchymatous, of hyaline isodiametric to elongate cells, marginal peridium cells (4.5–)7–13.5(–17) × (1.5–)2.5– 4.5(–6.5) μm (n = 46), basal peridium cells smaller, (3–)4–9 (–10) × 1.5–2.3(–2.7) μm (n = 16). Paraphyses unbranched, septate, thin-walled, collabent, 74–110 μm long, 4.0–7.5 μm wide at the base and gradually tapering to 2–4.5 μm at the tips (n = 20). Asci (94–)122–153(–175) × (2.8–)3.4–4.3(–5.2) μm (n = 98), unitunicate, long-cylindrical, with a short stipe, with eight ascospores arranged in a single fascicle, with an indistinct inamyloid apical apparatus. Ascospores (84–)118–149(– 170) × (0.6–)0.8–1.0(–1.3) μm, l/w = (35–)119–175(–205) (n = 55), filiform, with rounded ends, hyaline, without visible septa, without sheath or appendages. Colonies on CMD and MEA white; aerial hyphae abundant. No asexual morph observed.

Habitat and host range: Dead overwintered leaves of Fagus sylvatica and F. orientalis; rarely also on Quercus sp.

Distribution: Europe; known from France, Germany, Italy, Spain, and Switzerland.

Typification: France, without place, date and collector, on dead leaves of Fagus sylvatica, in Desmazières, Pl. Crypt. N. France, Ed. 1, no. 2098 (K(M) 206636, lectotype of Sphaeria ischnotheca here designated, MBT 390204; PC 0706583, isotype); same collection, in Desmazières, Pl. Crypt. N. France, Ed. 1, no. 1798 (K(M) 206635, PC 0706584, isotypes). Italy, Veneto, Treviso, near Conegliano, spring 1877, C.L. Spegazzini (PAD, holotype of Linospora faginea). Switzerland, Zürich, Thuraue near Flaach, 13 May 2017, L. Beenken (WU 40024, epitype of Sphaeria ischnotheca here designated, MBT 390205; ex epitype culture CBS 145761 = LIF1).

Other specimens examined: France, Calvados (14), Caen, on dead leaves of Fagus sylvatica, without date, M.R. Roberge (M-0304427,? syntype). Landes, Lussagnet, 43.763725° N, − 0.223289° E, 140 m, 16 May 2017, A. Gross (ZT Myc 59965). Germany, Bavaria, Freising, Kranzberger Forst, Weltwald, on dead leaves of Fagus orientalis, 30 Apr. 2019, L. Beenken (WU 40033). Spain, Asturias, Gijón, on dead leaves of Fagus sylvatica, 16 Apr. 2015, Enrique Rubio Domínguez ERD 6431 (WU 40027). Ibid., on dead leaves of Fagus sylvatica and Quercus robur, 16 Apr. 2015, Enrique Rubio Domínguez (WU 40026; culture LIF3). Switzerland, Zürich, Ellikon am Rhein, 20 May 2017, L. Beenken (WU 40025, ZT Myc 59966; culture LIF2). Zürich, Winterthur, Eschenberg, 47°28′58″ N, 8°43′ 24″ E, 530 m, 16 May 2015, L. Beenken (ZT Myc 59967).

Notes: DNA sequence data and morphology place the species within Xylariaceae, as closest relative of L. ochracea. Desmazières (1851) first included specimens from leaves of Fagus sylvatica in his Sphaeria ochracea, but soon thereafter, he described them as a distinct species, S. ischnotheca (Desmazières 1852). In the protologue, he mentioned that the type collection contained only immature asci without spores, which was confirmed for all syntypes investigated in our study. The type collection was edited and distributed in two sets as Pl. Crypt. N. France, Ed. 1, nos. 1798 and 2098, which is also mentioned in the protologue. Neither locality nor collector are mentioned on the herbarium labels and in the original description of the species, and no original notes of Desmazières are attached to the two copies present in PC. However, the herbarium labels of a specimen in M, probably also a syntype, indicates that it was collected by M.R. Roberge in Caen, i.e. the same place and collector as the type of L. ochracea (see below), which appears plausible considering that material of Fagus was mentioned in the original description of L. ochracea. As the type collection of Sphaeria ischnotheca is immature, we here designate a recent mature collection, for which a culture and DNA sequences are available, as epitype to stabilize the species nomenclature.

Linospora faginea, which was also described from dead leaves of Fagus sylvatica, is obviously a synonym of L. ischnotheca; the protologue in Saccardo (1878) fully matches our material. As Saccardo material of PAD is not sent out on loan, we have not been able to investigate the type in detail, but the illustrations of the specimen and label kindly provided by the Erbario dell’Università di Padua show that it agrees with L. ischnotheca (see Fig. 3d).

The inamyloid apical apparatus of L. ischnotheca is usually indistinct, and only well-seen in IKI (Fig. 3r) or cotton blue. For beautiful additional illustrations of the Spanish specimen ERD 6431, see also forum/35346.

Fig. 3 Linosporopsis ischnotheca. a Colonies (bleached patches) on dead overwintered leaves of Fagus sylvatica with scattered black, clypeus-like uniperitheciate pseudostromata. b–d Close up of colonies with black clypeus-like uniperitheciate pseudostromata. e–g Uniperitheciate pseudostromata from above (e), in side view (f), and in transverse section (g). h Host epidermis cells with dark brown, septate, branched hyphae forming a textura intricata. i Uniperitheciate pseudostroma in transverse section. j Pseudoparenchymatous, hyaline peridium and adjacent host tissue in section. k–o Asci (o immature). p–r Ascus apices. s Paraphysis. All in 3% KOH, except i, j, p, s in water; r in Lugol after KOH pre-treatment (a, e–g, m, n WU 40027; b PC0706583, isotype; c PC0706584, isotype; d PAD, holo- type of Linospora magnagutiana subsp. faginea; h K(M) 206638, isotype; i, j, p, s WU 40026; o, q, r K(M) 206636, lectotype). Scale bars a, d 10 mm; b 1 mm; c, e 200 μm; f, g, i 100 μm; h, j–o, s 10 μm, p–r 5 μm