Arthothelium aurantiacopruinosum Van den Broeck & 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 : 53-55

Arthothelium aurantiacopruinosum Van den Broeck & Ertz sp. nov. ( Fig.1F − J )

MycoBank 822912

The new species differs from all other Arthothelium species by black, orange pruinose ascomata in combination with ascospores of 34–42 × 10–14 μm and having two larger terminal cells.

Type: — DEMOCRATIC REPUBLIC OF THE CONGO. Oriental Province: Yangambi, Yangambi Man Biosphere Reserve, mixed tropical rain forest, on the bark of Scorodophloeus zenkeri , 400-450 m, 00°46’49.9”N, 24°31’15.9”E, 19 October 2013, D. Van den Broeck 6234 (holotype: BR!).

Thallus corticolous, crustose, inconspicuous to greenish to greyish-green, smooth, continuous. Prothallus black. Photobiont not observed, doubtfully lichenized. Ascomata 0.4–1.0 × 0.25–0.6 mm, numerous, slightly elevated above thallus level, rounded to slightly elongate, occasionally stellate, scattered more or less evenly over the thallus; disc black, partly or completely covered by orange pruina, K+ purplish, unchanged when wet, fragile, flat to convex, without visible margin. Excipulum inconspicuous. Epihymenium 30–40 μm thick, with a dark red-brown layer formed by the tips of the interascal hyphae, ca. 2–3.5 μm wide. Hymenium 50–80 μm tall, hyaline, inspersed with orange crystals, completely dissolving in K, I+ red, K/I+ blue. Paraphysoids hyaline, some with distinct brown caps and walls, branched and netted, ca. 1.8–2.0 μm wide. Hypothecium 30–50 μm thick, red-brown, inspersed with orange crystals, completely dissolving in K. Asci 50–65 × 45–50 μm (N = 4), globose to ovoid, 8-spored, an ocular chamber not observed, without a K/I+ blue ring structure in the tholus. Ascospores 34–42 × 10–14 μm (N = 25), muriform, persistently hyaline, ellipsoid, with two larger terminal cells, rest of the cells divided by 5–7 transversal and 1–2 longitudinal septa; gelatinous sheet not observed; spore ontogeny not observed. Pycnidia not observed. Thallus K–, C–, KC–, PD–, UV–. Calcium oxalate not observed. TLC (solvent B) revealed an unknown secondary metabolite UV+ greenish before heating (R f 10).

Distribution and ecology: —The new species is only known from tropical rain forests in the Congo Basin where it grows on bark of trees.

Etymology: —The epithet aurantiacopruinosum refers to the orange pruina on the ascomata.

Remarks: — Arthothelium spadiceum Müller Argoviensis (1892: 37) is described as possessing yellow to yellowish or black ascomata but without pruina ( Müller 1892). According to the description of Patwardhan & Makhija on the herbarium sheet of the isotype, the ascospores are persistently hyaline without a larger terminal cell and much broader (16–22 μm) than those of the new species (10–14 μm). A. endoxanthum Müller Argoviensis (1880: 44) is another species with yellowish-orange, becoming orange-brown, ascomata but they are linear, stellate branched and the ascospores have also no larger terminal cell ( Müller 1880; description of Patwardhan & Makhija on the herbarium sheet of the type). Two other species of Arthothelium with terminal cells larger at both ends are A. subilicinum (Leighton 1869: 181 in Leighton 1871) Zahlbruckner (1922: 136 in Zahlbruckner 1924) and A. follmannii C.W. Dodge (1966: 311 in Dodge 1967). A. subilicinum differs from A. aurantiacopruinosum by much broader (15–20 μm) ascospores and a greenish-brown epihymenium ( Makhija & Patwardhan 1995b). A. follmannii is characterized by black epruinose ascomata on a thick white thallus and a trentepohlioid photobiont ( Dodge 1967).

Several Arthonia species like A. elegans ( Acharius 1810: 135) Almquist (1880: 19) (H!), A. borbonica Ertz, Elix & Grube (2010: 222) (BR!), A. ferruginea Vainio (1890:165) (M!), A. karunaratnei Weerakoon & Aptroot (2016: 133 in Weerakoon et al. 2016), A. ochrocincta Nylander ex Willey (1890: 8) , A. ochrodes Nylander ex Willey (1890: 10) (H!), A. rubiginella Nylander (1900: 19) (H!) and A. leucographella Müller Argoviensis (1888a: 178) have also orange pruinose ascomata but the ascospores have only transversal septa ( Almquist 1880; Müller 1888a; Vainio 1890; Willey 1890; Nylander 1900; Ertz et al. 2010; Weerakoon et al. 2016).

A second specimen with black, orange pruinose ascomata and the same chemistry was found in the Democratic Republic of the Congo in Kisangani, forest reserve of Masako, on a big tree of Gilbertiodendron dewevrei (D. Ertz 14924, BR). That specimen differs from the new species by ascospores with only one larger terminal cell but the specimen is in poor condition. All the ascospores are more or less degenerated and most of them have a brown colour. It is unclear if this specimen represents a further new species or not.

Figures

FIGURE 1. New species of Arthothelium from Africa. Arthothelium atrorubrum (A−E, holotype), Arthothelium aurantiacopruinosum (F−J, holotype), A−B, F−G. Thallus with apothecia. C−E, I & J. Ascospores. H.Ascus in water. Scale inA, F = 1000 μm, in B = 500 μm, in C−E, I & J = 10 μm, in G = 250 μm, in H = 20 μm.