Parmotrema paramascarenense D.M. Masson, 2024

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 : 86-88

Parmotrema paramascarenense D.M. Masson , sp. nov.

MycoBank no. 853877

Diagnosis. Similar to P. mascarenense but differs from it by the presence of soredia instead of isidia. Holotype:— FRANCE. Réunion: Cilaos, Ravine des Calumets , elev. 1310 m, 21°09’06”S, 55°29’39”E, in leeward montane rainforest, in an overall south orientation, on ± mossy bark of a trunk of Melicope obtusifolia , 21 August 2012, D. Masson 974.3938 (MNHNPC-PC0088080).

( Fig. 33 )

Thallus foliose, moderately adnate, membranaceous to subcoriaceous, up to 11 × 13 cm. Lobes imbricate, irregular, 3–8 mm wide; lateral lobes, especially when sorediate, frequently erect and revolute, and forming complex T-shaped structures with age; margins sinuate, dentate to laciniate, occasionally lobulate, irregularly ciliate or eciliate ( Fig. 33E ). Cilia black, scarce to almost absent, mostly unevenly distributed at the lobe margins, often ± in groups, simple to 3 times branched, ca. 0.03–0.06 mm in diameter at the base, up to 3 mm long. Upper surface pale greenish grey, rather dull, rugose, distinctly effigurate white-maculate, old parts finely cracked, sometimes with a subreticular pattern; sorediate, lacking isidia, schizidia, pustules, dactyls. Soralia at first terminal at the apex of tiny laciniae, then ± labriform or subcapitate, finally ± spreading submarginally, mostly when the lobes become revolute ( Fig. 33D ); in old parts, sorediate laciniae may develop into arbuscular structures (‘sorediate arbusculae’ of Spielmann & Marcelli 2020), up to 5 mm long ( Fig. 33C ). Soredia subgranulose to granulose, (40)– 49.8 –(70) µm in diameter (n = 60, from 2 specimens, SD = 6.8 µm). Laciniae frequent, marginal, simple or somewhat branched, sorediate, up to 2 × 4 mm. Lobules occasional, marginal, up to 5 × 6 mm. Medulla white throughout. Lower surface smooth or rugulose, granulose in places, ± cracked, shiny, duller in the central part, black to the margin, or with a chestnut brown erhizinate marginal zone (ca. 1.5–5 mm wide) at main lobe tips, sorediate lateral lobes often with an erhizinate, ivory white or ivory-mottled marginal zone (1–2 mm wide), underside of sorediate laciniae often ivory white or cream ( Fig. 33D ). Rhizines in ± scattered groups, concolor to the lower surface, simple, very rarely furcate, up to 1.5 mm long. Apothecia not present. Pycnidia not present. Upper cortex palisade plectenchymatous, not fragile, (13)– 18.4 –(27) µm thick. Algal layer here and there briefly interrupted, (10)– 17.4 –(23) µm thick. Medulla (62)– 69.9 –(90) µm thick. Lower cortex prosoplectenchymatous, (16)– 17.9– (20) µm thick.

Chemistry:— Spot tests and fluorescence: upper cortex K+ yellow, UV−; medulla K+ slowly orange brown, C−, KC−, P+ orange, UV−. Secondary metabolites (TLC): upper cortex with atranorin and chloroatranorin; medulla with succinprotocetraric acid (major) and fumarprotocetraric acid (minor).

Etymology: — From the Greek para, near or beside, a reference to the very similar, but isidiate, P. mascarenense .

Geographical distribution:—So far only known from three collections from Réunion, and one from Madagascar. For Réunion, the exact location of the oldest collection (1989) is unfortunately unknown. The two others come from the Cirque de Cilaos, in the southern part of the Piton des Neiges massif, between 1300 and 1500 m ( Fig. 33A ). The Madagascan collection site is located in the central part of the Central Highlands, at an elevation of 1610 m.

Ecology:— The four specimens examined were corticolous. The holotype was found on the more or less mossy bark of a trunk of Melicope obtusifolia (DC.) T.G. Hartley , a tree endemic to Réunion and Mauritius ( Hartley 2001), at 1.8 m above the ground. The habitat is a leeward montane rainforest in a ravine, with a general southern orientation. The bioclimate of the locality is pluvial tropical, thermotype belt = lower mesotropical (It = 430), ombrotype belt = upper humid (Io = 11.1) ( Fig. 33B ). The bioclimate of the Malagasy locality is pluviseasonal tropical, with thermotype belt = lower mesotropical (It = 442), ombrotype belt = lower humid (Io = 8.3) .

Notes:—This taxon is very similar to Parmotrema mascarenense , both morphologically and chemically. It differs only by the nature of the vegetative propagules, soralia instead of isidia. This is reminiscent of the case of P. nephophilum in Réunion, where a widespread isidiate/phyllidiate form is sympatric with a much less frequent sorediate form. It could be that P. paramascarenense is only a morphotype of P. mascarenense . Unfortunately, no molecular data could be obtained for the sorediate form, despite two attempts to extract DNA from the most recent sample. It is therefore not possible to test this hypothesis, unlike in the case of P. nephophilum . We therefore treat this sorediate form as a separate species pending further study, as suggested by Lücking et al. (2021).

Only two sorediate species with a maculate upper surface and containing succinprotocetraric acid as a major extrolite have been described so far in Parmotrema . The New Caledonian P. pustulatum Louwhoff & Elix differs from P. paramascarenense by its sorediate pustules and the additional presence of protocetraric acid as minor medullary substance ( Louwhoff & Elix 2000, 2002). The South American P. succinreticulatum (Eliasaro & Adler) Blanco et al. seems to be the sorediate counterpart of the isidiate P. sanctae-candidae , in the same way as the P. paramascarensense / P. mascarenense pair. It differs mainly from P. paramascarenense by the strong reticulate maculation on the upper surface, and the rhizines that often extend to the lobe margins ( Eliasaro & Adler 1997, Eliasaro 2001).

Additional specimens examined (paratypes):— FRANCE. Réunion: without locality, April 1989, G. Follmann & I. Follmann-Schrag s.n. (B); Cilaos , Rundweg von Thermales zum Roche Merveilleuse, elev. 1400–1500 m, 21°07’S, 55°28’30”E, in kümmerlichen Primärwald-Resten, 20 August 1991, K. & A. Kalb 33656 ( WIS) .

MADAGASCAR. Analamanga: Manankazo, lambeau forestier de Farazana, km 133 route de Majunga, elev. 1610 m, [18°09’S, 47°13’E], forêt claire, tronc d’arbre, 20 August 1956, H. des Abbayes 2666 ( REN 000056 ) .

Figures

FIGURE 33. Parmotrema paramascarenense. A: Distribution on Réunion (UTM 2×2 km grid system); B: Bioclimatic characteristics of collection sites (abbreviations and threshold values for thermotype and ombrotype horizons from Rivas-Martínez et al. 2011: 17–18); C: Sorediate arbusculae in old part of thallus (holotype); D: Soralia at the apex of tiny laciniae, ± labriform or subcapitate, in young part of thallus (holotype); E: Gross morphology of thallus (Kalb & Kalb 33656). Scale bars: A = 10 km; C, D = 4 mm; E = 8 mm.