Thelotrema pachysporoides Dantas, Lücking & M. Cáceres, 2017

Dantas, Jaciele De Oliveira, Alves, Elaine Santos, Lücking, Robert & Cáceres, Marcela Eugenia Da Silva, 2017, Three new species of Graphidaceae (lichenized Ascomycota) from the semi-arid region of northeast Brazil, Phytotaxa 331 (2), pp. 289-294 : 292-293

Thelotrema pachysporoides Dantas, Lücking & M. Cáceres , sp. nov. Fig. 1I–L

Mycobank No.: MB 822331.

Diagnosis: Differing from Thelotrema pachysporum in the small ascospores and from T. fuscosubtile in the ecorticate thallus and smaller, distinctly brown ascospores.

Type: BRAZIL. SERGIP E: Fazenda Santa María da Lage ; 10º44’37” S, 38º05’44” W, 390 m; isolated remnant of Caatinga vegetation, on tree bark; 28 January 2015, J. Dantas ( ISE 30802 — holotype) ; ibid., J. Dantas ( ISE 30801 — paratype) .

Etymology: The epithet refers to the similarity with Thelotrema pachysporum .

Description: Thallus corticolous, epiperidermal, up to c. 5 cm diam., continuous; surface uneven, white-grey to pale yellowish grey; prothallus absent. Thallus in section 50–100 μm thick, ecorticate or in part with a loose cortex, 5–10 μm thick, with thick photobiont layer 40–80 μm thick, interspersed with clusters of calcium oxalate crystals. Photobiont Trentepohlia ; cells rounded to irregular in outline, in irregular groups, yellowish green, 8–12 × 6–9 μm. Ascomata rounded, erumpent to prominent, 0.25–0.4 mm diam., 0.15–0.2 mm high; disc partially covered by 0.15–0.25 mm wide pore, grey-brown, thickly white-pruinose; proper margin thin, entire, separated from the thalline margin by a narrow split, forming an indistinct, white rim around the disc; thalline margin thick, smooth to uneven, white-grey to pale yellowish grey. Excipulum entire, pale yellow, 10–20 μm wide, paraplectenchymatous, separated from covering thalline layer by a split; laterally covered by algiferous thallus, 40–60 μm thick; columella absent; hypothecium prosoplectenchymatous, 10–20 μm high, hyaline; hymenium 90–100 μm high, hyaline, clear; epihymenium 5–10 μm high, grey-granular, granules not soluble in K. Periphysoids present, 20–30 μm long; asci fusiform, 70–80 × 15–20 μm. Ascospores 8 per ascus, ellipsoid, 7–13-septate, 25–35 × 7–10 μm, 3–4 times long as wide, becoming brown, distoseptate with lens-shaped lumina, I+ weakly violet-blue when immature. Secondary chemistry: No substances detected by TLC.

Distribution and ecology: Thus far only known from the state of Sergipe in northeast Brazil, growing on tree bark in an isolated Caatinga remnant.

Characterization and taxonomic relationships: Thelotrema pachysporoides belongs in the T. monosporum group, characterized by a whitish, ecorticate thallus and brown ascospores ( Rivas Plata et al. 2010, 2013). It is most similar to T. pachysporum Nyl. (hence the specific epithet), which differs in the larger ascospores (35–75 × 9–13 μm). The Australian Thelotrema fuscosubtile Mangold, Lücking & Lumbsch ( Mangold et al. 2014) is partially (loosely) corticate, has ascomata with a thicker thalline margin and very distinct proper margin, and produces slightly larger ascospores (35–50 × 7–10 μm), which remain hyaline for a long time and eventually become pale brown.

Figures

FIGURE 1. Graphis alba (A, ISE 38000, paratype; B–C, ISE 38003, holotype). A–B. Thallus with lirellae showing conspicuous white labia cover. C. Ascospore. Halegrapha redonographoides (holotype). D–F. Thallus with more or less pseudostromatic lirellae, the reddish portions indicating decomposing norstictic acid; G–H.Asci with ascospores.Thelotrema pachysporoides (I, ISE 38001, paratype; J–L, ISE 38002, holotype). I–K. Thallus with apothecia; L. Ascus with ascospores. Scale in A–B, D–F, I–H = 1 mm, in C, G–H, L = 10 μm.