Parmotrema mwaliense D.M. Masson

Masson, Didier, Magain, Nicolas & Sérusiaux, Emmanuël, 2024, Small island but great diversity: thirty six species of Parmotrema (Parmeliaceae, lichenized Ascomycota), including sixteen new species, on Réunion (Mascarenes), with additional data from the Western Indian Ocean, Phytotaxa 657 (1), pp. 1-138 : 122-123

Parmotrema mwaliense D.M. Masson , sp. nov. MycoBank no. 853881

Diagnosis. Characterized by the ciliate margin of the lobes, the numerous elongate, canaliculate and branched laciniae, the lack of vegetative propagules, the perforate disc of the apothecia, and the presence of diffractaic and barbatic acids in the medulla.

Holotype:— COMOROS. Mohéli: massif de Mafondrodjo [= Mafoumboudjou], elev. 500–600 m, epiphyte, June 1945, unknown collector ( REN 000048 ).

( Fig. 44 )

Thallus foliose, moderately adnate, subcoriaceous, ca. 8 × 8 cm (thallus fragmented). Lobes irregularly branched, imbricate, 2–7 mm wide; margins highly laciniate, very rarely lobulate, ciliate ( Fig. 44B ). Cilia frequent, black, mostly irregularly distributed at the lobe margins and at the margin of laciniae, simple to ± dichotomously 1–(2) times branched, ca. 0.03–0.08 mm in diameter at the base, up to 3 mm long. Upper surface ± shiny, emaculate to faintly white-maculate, clearly punctiform white-maculate on the amphithecia, smooth to rugose, here and there cracked, but not flaking, lacking schizidia, pustules, dactyls, isidia, and soralia. Laciniae numerous, marginal, very rarely laminal, elongate, generally canaliculate with ± subterete apex, ± dichotomously and repeatedly branched, margins ciliate, up to 16 mm long and 1.2 mm wide ( Fig. 44A ). Lobules rare, marginal, ciliate, up to 0.7 × 0.8 mm. Medulla white throughout. Lower surface smooth to rugose, fairly shiny; black to the margin, or with a brown or buff erhizinate marginal zone (ca. 2–3 mm wide) at main lobe tips; generally fully ivory white or mottled with black under the laciniae. Rhizines of variable density, unevenly distributed, black, simple, up to 1.5 mm long. Apothecia common, submarginal, up to 12 mm in diameter, shortly stipitate on constricted stipes; disc perforate, reddish brown, ± shiny, first concave, then ± flattening with age; thalline margin soon dentate, then laciniate with age ( Fig. 44A ); amphithecium smooth to verruculose, white-maculate; hymenium s. lat. (125)– 129.1 –(135) µm high, proper exciple with hyaline layer (8)– 10.3 –(13) µm high, intermediate layer (11)– 12.8 –(16) µm high, cortex-like basal layer (13)– 15.3 –(20) µm high. Ascospores 8 per ascus, simple, colourless, ellipsoidal, 22.5– 25.6 –29(29.5) × 12.5– 14.6 –17.5(18) µm, Q = 1.39– 1.76 –2.13(2.15), epispore (2)– 2.2 –(3) µm thick, n = 30. Pycnidia numerous, mainly on laciniae, but also submarginal on lobes; black. Conidia not found (20 pycnidia investigated). Upper cortex palisade plectenchymatous, not fragile, (15)– 22.3 –(32) µm thick. Algal layer continuous, (18)– 22.7 –(28) µm thick. Medulla (90)– 123.5 –(145) µm thick. Lower cortex prosoplectenchymatous, (10)– 12.0– (14) µm thick.

Chemistry:— Spot tests and fluorescence: upper cortex K+ yellow, UV−; medulla K−, C−, KC−, P−, UV+ white. Secondary metabolites ( TLC): upper cortex with atranorin and chloroatranorin; medulla with diffractaic acid (major) and barbatic acid (submajor). Etymology:—Named after the island of origin, Mwali (Mohéli in Comorian).

Geographical distribution:— So far only known from the type locality on the island of Mohéli, in the Comoro Archipelago in the Indian Ocean .

Ecology:—The only available specimen was collected at around 500–600 m a.s.l., on bark, and most probably, according to the locality cited, in the dense mid-elevation evergreen rainforest occupying the central part of the island between 500 and 790 m elevation.

Notes:—In the genus Parmotrema , the simultaneous occurrence of both diffractaic and barbatic acids in the medulla is rare and only found in five or six species [the recently described P. neodiffractaicum R.S. Egan is likely to be conspecific with P. matudae (Kurok.) Hale ex DePriest & B.W. Hale ]. Of these, only the neotropical P. mesogenes (Nyl.) Hale and the Papuan P. praeinsuetum (Kurok.) Louwhoff & Elix lack vegetative propagules like P. mwaliense ( Kurokawa 1984, Elix 1995, Louwhoff & Elix 1999, Egan et al. 2016). However, both taxa are devoid of the distinctive laciniae of P. mwaliense and have an imperforate apothecial disc. Furthermore, the lobe margins of P. mesogenes are eciliate and its medulla is pigmented. The medulla of P. praeinsuetum contains protocetraric acid in addition to diffractaic and barbatic acids, and its ascospores are narrower (10–13.5 µm wide, according to Kurokawa 1984 and Louwhoff & Elix 1999) than those of P. mwaliense (12.5–17.5 µm wide). The morphology of the thallus and the size of the ascospores of P. appendiculatum are quite similar to those of P. mwaliense , but the apothecial disc of P. appendiculatum is imperforate and its medulla is coloured yellow by secalonic acid A and does not contain diffractaic acid.

The type collection of P. mwaliense was cited and illustrated by des Abbayes (1956: 11–12) under the name Parmelia melanothrix var. lacinulata Müll. Arg. However , the latter taxon has a light brown underside and contains alectoronic acid ( Müller 1891, Hale 1965a; image of the isotype in G).

Figures

FIGURE 44. Parmotrema mwaliense (holotype). A: Part of thallus showing the ciliate margin of the lobes, the numerous elongate, canaliculate and branched laciniae, and a mature apothecium with a perforate disc; B: Another part of thallus with ciliate and laciniate lobe margins. Scale bars: A, B = 5 mm.