Arthothelium atrorubrum 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 : 52-53

Arthothelium atrorubrum Van den Broeck & Ertz sp. nov. ( Fig.1A − E )

MycoBank 822911

The new species differs from all other Arthothelium species by black ascomata with abundant red or purplish pigment in the hypothecium in combination with submuriform ascospores of 13–17 × 7–10 μm without larger terminal cells.

Type: — MADAGASCAR. Province Diego Suarez: Antsiranana, W of Sambava, Marojejy National Park, along trail from Camp Simpona to summit, rather dense humid montane forest grading into dense sclerophyllous upper montane forests, ca. 1600 m, 14°26’27”S, 49°44’23”E, 20 October 2014, D. Ertz 20071 (holotype: BR!, isotype: TAN).

Thallus corticolous, crustose, whitish, sometimes with areas having a reddish to purplish tinge or speckled with reddish to purplish granules, continuous or rimose, slightly shiny, ca. 100–200 μm thick. Prothallus black. Photobiont not observed, doubtfully lichenized. Ascomata 0.35–2.5 × 0.25–1.75 mm, numerous, first immersed in the thallus, bursting through it to become sessile, irregularly rounded, sometimes shortly elongated or lobate, scattered more or less evenly over the thallus or grouped; disc black, frequently red or purplish at the margins or where the (epi)hymenium is abraded or cracked owing to abundant red pigment in the hypothecium, with or without a whitish pruina (probably consisting of remnants of thallus), unchanged when wet, shiny, ± rough, flat to slightly convex, without visible margin. Excipulum inconspicuous. Epihymenium 20–25 μm thick, with a dark brown layer formed by the tips of the interascal hyphae, K+ green. Hymenium 60–70 μm tall, hyaline to slightly brownish, not inspersed, I+ red, K/I+ blue. Paraphysoids hyaline, some with distinct dark caps and walls, densely branched and netted, ca. 1–1.5 μm wide. Hypothecium 65–85 μm thick composed of red granules or crystals, K+ purplish, not dissolving, I+ red, K/I+ blue. Asci 17–19 × 16–18 μm (N = 5), globose to ovoid, without or with a very short stipe, 8-spored, some asci with broad or very small ocular chamber, with K/I+ blue ring like structure in the tholus. Ascospores 13–17 × 7–10 μm (N = 22), submuriform, hyaline, becoming dark brown (wall, including septa) when overmature, oblong, usually without enlarged terminal cell, with 3(–4) transversal and 1 longitudinal septa; gelatinous sheet ca. 0.5 μm; spore ontogeny macrocephalic, bidirectional. Pycnidia partly immersed in thallus, rare, forming conical-hemispherical projections, ca. 1.3 mm high, the ostiole sometimes visible, black, mostly without conidia, composed of brown walled hyphae (K+ green), intermingled with orange pigment (K+ purplish), hyphae ca. 2–3 μm. Conidia 7–15 × 1–1.8 μm, hyaline, non-septate, straight, bacilliform. Thallus K–, C–, KC–, PD+ yellow to orange, UV–. Calcium oxalate not observed. Three secondary metabolites were detected by TLC (solvent B): an unknown metabolite UV+ turquoise, before and after heating (R f 7), psoromic acid (brown colour, R f 43) and a third unknown metabolite at R f 49 with an UV+ greyish-white colour before and after heating.

Distribution and ecology: —So far Arthothelium atrorubrum is only known from northern Madagascar, and seems restricted to the Marojejy National Park. This corticolous species inhabits rather dense humid montane forests where it might be locally abundant.

Etymology: —The epithet atrorubrum refers to the blackish colour of the ascomata and the reddish pigment in the hypothecium.

Remarks: —In a recent preliminary checklist, 500 lichen species are reported from Madagascar ( Aptroot 2016). In this list only two species of Arthonia , both foliicolous are mentioned, but not a single species of Arthothelium is included.

Several Arthothelium species have red coloured ascomata: A. coccineonigrum Makhija & Patwardhan (1995b: 207) , A. coccineum Müller Argoviensis (1893a: 108) , A. gregarinum ( Willey 1887: 53) Zahlbruckner (1903: 91) (= Coniarthonia gregarina (Willey) Grube 2001: 496 ), A. miltinum ( Krempelhuber 1875: 42 in von Krempelhuber 1875) Müller Argoviensis (1886: 316) and A. sanguineum ( Nylander 1885: 311) Zahlbruckner (1903: 91) but they have all persistently hyaline and larger ascospores (17–46 μm long) ( Nylander 1885; Müller 1886, 1893a; Makhija & Patwardhan 1995b; Grube 2001). Arthonia erythrogona Müller Argoviensis (1893c: 157) described from Costa Rica and also mentioned from Tanzania ( Müller1894a) is similar to the new species by a white thallus speckled with reddish granules, black ascomata with red pigment at the margins, internally with red granules or crystals, but the ascospores are transversally 3–4-septate, 11–13 × 5–6 μm, with two enlarged end cells ( Müller 1893a). A study of the type specimen (BR!) revealed that the red pigment in the ascomata reacts K+ purplish, not dissolving, ascospores that are transversally 3-septate, 12–13.5 × 4–4.5 μm. A trentepohlioid photobiont is clearly present.

The new species is also similar to Arthonia purpurissata Nylander (1863a: 482) which differs by smaller dark brown globose ascospores (8–9 × 7–8 μm) ( Nylander 1863a).

Stizenberger (1891) mentioned the collection of Arthonia macrotheca Fée (1837: 42) (= Arthothelium macrothecum (Fée) A. Masssalongo (1852: 55) by Hildenbrandt from Madagascar during his expedition 1879–1881 ( Beentje 1998). This species is characterized by black ascomata without any red pigment ( Fée 1837). The type of A. macrothecum (G!) from South America has been seen by us but not the material collected in Madagascar by Hildenbrandt. Nevertheless one of us has collected a specimen in Madagascar that agrees well with the type of A. macrothecum (D. Ertz 19744), confirming its presence in Madagascar.

Additional specimens examined: — MADAGASCAR. Province Diego Suarez: Antsiranana, W of Sambava, Marojejy National Park , along trail from Camp Simpona to summit, rather dense humid montane forest grading into dense sclerophyllous upper montane forests, corticolous, ca. 1500 m, 14°26’19”S, 49°44’29”E, 20 October 2014, D. Ertz 20026 (BR) ; corticolous, ca. 1600 m, 14°26’27”S, 49°44’23”E, 20 October 2014, D. Ertz 20066 (BR), D. Ertz 20078 (BR); along trail from Camp Marojejia to Camp Simpona , rather dense humid montane forest, ca. 1000 m, 14°26’13.5”S 49°45’19.7”E, 19 October 2014, D. Ertz 19950 (BR) .

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.