Arthothelium miesii Van den Broeck, Tehler & Ertz, 2017

Broeck, Dries Van Den, Tehler, Anders, Razafindrahaja, Tahina & Ertz, Damien, 2017, Four new species of Arthothelium (Arthoniales, Ascomycetes) from Africa and Socotra, Phytotaxa 331 (1), pp. 51-64 : 56-59

Arthothelium miesii Van den Broeck, Tehler & Ertz sp. nov. ( Fig.2G − N )

MycoBank 822914

The new species differs from all other Arthothelium species by the combination of a thick thallus with immersed, brown to yellowish, stellate to cerebriform, slightly to heavily greyish pruinose ascomata in combination with submuriform, persistently hyaline, ascospores of 16.5–21 × 7–10 μm without larger terminal cells and filiform conidia of 11–21 × 0.5–2 μm.

Type: — YEMEN. Socotra: Aden, on top of the Hamaderoh Plateau, on hard dolomitic limestone, 400 m, 12°36 N, 54°17 E, 23 March 1997, B. Mies 805a (Herb. No. 14131) (holotype: FR!).

Thallus saxicolous or corticolous, crustose, pale cream, sometimes speckled with orange spots of unknown origin and composition, rimose-areolate, cretaceous, up to ca. 1 mm thick, areoles flat to slightly or very convex, very variable, medulla white, filled with many cubic crystals, 1–20 μm wide. Prothallus not observed. Photobiont cells rounded, ellipsoid to rectangular with greenish content, without orange pigments, trentepohlioid, cells 7.5–16.0 × 6.5–12.0 μm. Ascomata up to 2–3 mm diam., numerous, immersed in elevated convex areoles, stellate to cerebriform, with lobes/ ramifications of 0.30–1.55 × 0.30–0.70 mm; disc brown to yellowish, of a soft texture, slightly or heavily greyish pruinose, wet ± transparent, sometimes surrounded by whitish thallus tissue. Excipulum inconspicuous. Epihymenium 25–30 μm thick, hyaline, patchily inspersed with orange crystals, completely dissolving in K. Hymenium 55–70 μm tall, I+ blue turning rapidly into orange to red, K/I+ deep blue. Paraphysoids hyaline, richly branched and netted, ca. 1.5 μm wide, often with swollen apices and dark caps up to 2.5 μm wide. Hypothecium 60–100 μm thick, hyaline, densely inspersed with orange crystals, completely dissolving in K, immediately I+ orange to red, K/I+ deep blue. Asci 45–65 × 20–30 μm (N = 5), ovoid, with a distinct stipe, 8-spored, no distinct ocular chamber observed, a K/I+ blue ring like structure in the tholus observed in one ascus. Ascospores 14–21 × 7–10 μm (N = 15), submuriform, persistently hyaline, ellipsoid, with 5(–7) transversal and 1 longitudinal septa; gelatinous sheet 0.5 μm, not always observed; spore ontogeny macrocephalic, bidirectional. Pycnidia abundant, blackish, immersed in pits, rounded, sometimes covered by thallus tissue. Conidia hyaline 11–21 × 0.5–2 μm (N = 12), filiform, mostly curved to sickle-shaped, occasionally ± straight. Thallus cortex K± yellow, C–, KC–, PD+ yellow, UV–, N–; medulla PD+ yellow, K–, N–. Calcium oxalate crystals quadrangular, abundant. One unknown secondary metabolite (UV+ dark violet spot with orange-yellow halo after heating) with R f value 43 in B and 52 in C.

Distribution and ecology: — Arthothelium miesii is only known from Socotra were it has several times been collected on rocks and once on bark.

Etymology: —This new species is dedicated to Bruno Mies, the collector of the type specimen, for his effort to investigate the lichen biota of Socotra.

Remarks: —In an extensive study of the lichen biota of Socotra, Mies and Schulz (2004) attributed all the saxicolous specimens of Arthothelium to the Mediterranean A. crozalsianum B. de Lesdain in de Crozals (1924: 112) , a synonym of Arthonia albopulverea Nylander (1853: 319) according to Sundin (1999), pending a thorough revision of the genera Arthothelium and Arthonia . According to our observations of the lectotype (H!) this species strongly differs from A. miesii by a thin thallus (up to 0.2 mm), doubtfully lichenized, lirellate ascomata, hymenium I+ blue, turning rapidly into red and an olivaceous brown to reddish brown epihymenium.

Arthothelium abnorme ( Acharius 1810: 259) Müller Argoviensis (1880: 287) was also reported from Socotra ( Steiner 1902) while two other species were described as new to science. A. emersum Müller Argoviensis (1882: 469) was described from material collected in Socotra by Prof. Bayley Balfour and Dr. Schweinfurth while Steiner described A. variabile J. Steiner (1902: 101) from the material collected in Socotra and Simha by O. Simony in 1898 and in 1899. According to our observations of the type (BM!), A. abnorme differs from the new species by epruinose brown to black ascomata, I+ blue hymenium, a dark brown epihymenium and smaller ascospores (5–8 μm broad instead of 8–10 μm) and, a different chemistry (according to Makhija & Patwardhan (1995b) no secondary metabolites were revealed by TLC). The lectotype (G!) of A. emersum is characterized by simple, rounded to elliptical but never lobate, erumpent brownish black ascomata, I+ blue hymenium, a dark brown epihymenium and a different chemistry, (according to Makhija & Patwardhan (1995b) no secondary metabolites revealed by TLC).

The type of Arthothelium variabile (WU!) is present on two branches. On the largest branch two distinct thalli are present. One of them has a whitish thallus with a black prothallus and with brown immersed pycnidia, either solitary or grouped by two, and having a wide open ostiole. The second thallus is inconspicuous, without prothallus and has immersed blackish-brown irregular ascomata with muriform ascospores. No conidia were found on this thallus. Probably the thallus with conidia belongs to another species. In comparison with A. miesii , A. variabile has epruinose, occasionally with some remnants of thallus, irregular, but not cerebriform, blackish-brown ascomata and larger ascospores (20–32 μm in length).

Seven species of Arthonia are mentioned or described from Socotra ( Brown & Mies 2012): A. stictaria Nylander (1867a: 440) is a lichenicolous fungus ( Nylander 1867a). The other six species are lichens with only transversely septate ascospores: A. applanata Stizenberger (1891: 198) (= A. complanatula Müller Argoviensis1882: 468 ), A. calospora Müller Argoviensis (1882: 468) , A. cinnabarina (de Candolle 1805: 323 in de Lamarck & de Candolle 1805) Wallroth (1831: 320) (= Coniocarpon cinnabarinum ), A. perpallens Nylander (1863b: 231) , A. polymorpha Acharius (1814: 7) , A. speciosa (Müller Argoviensis 1894a: 286) Grube (2007:58) ( Nylander 1863b; Müller 1882, 1887b; Grube 2007).

At present ten Arthothelium species with a saxicolous habitat are known. Morphologically, chemically and anatomically the new species is most similar to A. desertorum , a species known from Namibia and Galapagos ( Aptroot & Wirth (2006). According to these authors this species contains divaricatic acid. TLC performed by us on A. miesii (solvents B en C) revealed the presence of one unknown secondary metabolite (UV+ dark violet spot with orange-yellow halo after heating) with R f value 43 in B and 52 in C, far below that of divaricatic acid (R f 53 in B and R f 67 in C) and just above that of psoromic acid in B (R f 40). The same secondary metabolite (thus not divaricatic acid) and calcium oxalate has been found by us in A. desertorum that differs from A. miesii by ascomata never becoming distinctly cerebriform, hymenium I+ blue, bacilliform, straight to slightly curved conidia, ascospores with 1–2 longitudinal and 4–5 transversal septa, becoming brown (dark brown when overmature). The size of the conidia in the protologue of A. desertorum is 6–8 × 0.8–1.0 μm according to Aptroot & Wirth (2006) whilst we observed conidia of 4.0–5.6 × 0.9–1.6 μm. Contrary to the protologue, ascospores with more than two longitudinal septa were not observed (N = 20). The picture in the protologue shows also not more than two longitudinal septa in the ascospores.

The ascospores of Arthothelium feuereri Aptroot & Seaward (2004: 119 in Seaward & Aptroot 2004) are characterized by a larger terminal cell and are much larger (40–50 × 20–25 μm) ( Seaward & Aptroot 2004). Allarthothelium elliotti ( Vainio 1896: 263) Zahlbruckner (1907: 241) , Arthothelium diffluens ( Nylander 1888b: 17) Imshaug & Fryday (2002: 422 in Fryday 2002), A. evanescens Øvstedal (2001: 554 in Øvstedal & Gremmen 2001) and A. halophilum Follmann (1968: 373) have also much larger ascospores (exceeding 20 μm in length) ( Vainio 1896; Follmann 1968; Øvstedal & Gremmen 2001; Fryday 2002). The other four saxicolous species, A. galapagoense Huneck & Follmann (1969: 169) , A. pacificum Follmann (1968: 375) , A. spilomatoides ( Nylander 1855: 169) Zahlbruckner (1922: 135) in Zahlbruckner 1924) and A. saxicolum Makhija & Patwardhan (1997: 169) , have a different chemistry and an hymenium that reacts I+ blue ( Nylander 1855; Follmann 1968; Huneck & Follmann 1969; Makhija & Patwardhan 1997).

Arthothelium chilense C.W. Dodge (1966: 311 in Dodge 1967) and Mycarthothelium angustissimum Vainio (1930: 169 in Vainio 1929 –1930), both with persistently hyaline ascospores of 18–21 × 6–10 μm differ from the new species by a dark brown epihymenium and 1–2 longitudinal septa. Moreover A. chilense has round to oblong ascomata and in M. angustissimum the photobiont is absent ( Vainio 1929 –1930; Dodge 1967).

Additional specimens examined: — YEMEN. Socotra : Sefflah, the ridge just S of the village on S coast at the E most part of the island, on limestone, 400–600 m, 12°30,723’N, 54°26,037’E, 24 March 2008, A. Tehler 9345 (S) ; in the southern part of the island along the road where it leads up into the mountains from the south, saxicolous, 300 m, 12°23.115’N 53°55.628’E., 23 March 2008, A. Tehler 9328 (S); corticolous, A. Tehler 9330 (S); Homill , in the eastern part of the island, on the ridge facing the sea E, saxicolous, 400–450 m, 12°35.472’N 54°18.693’E, 22 March 2008, A. Tehler 9321 (S) .

Figures

FIGURE 2. New species of Arthothelium from Africa and Socotra. Arthothelium frischianum (A−F, holotype), Arthothelium miesii (G−N, holotype). A−B, G−H. Thallus with apothecia. C, I. Ascus in water. D−F, J−N. Ascospores. Scale in A, G = 1000 μm, in B, H = 500 μm, in C = 25 μm, in D−F, I = 10 μm, in J−N = 5 μm.