Parmotrema meiospermum (Hue) D.M. Masson & Sérus. 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 : 57-59

Parmotrema meiospermum (Hue) D.M. Masson & Sérus. , comb. nov. MycoBank no. 853882

Parmelia internexa f. meiosperma Hue (1899: 185) MycoBank no. 459067

Type:— FRANCE. La Réunion: Mafate, 1889, frère Rodriguez s.n. (MNHN-PC-PC0728355!, lectotype designated by Hale 1976) .

≡ Parmelia meiosperma (Hue) C.W. Dodge (1959: 139) MycoBank no. 368689

≡ Pseudoparmelia meiosperma (Hue) Hale (1974c: 190) MycoBank no. 343414

( Fig. 23 )

Thallus foliose, moderately adnate, membranaceous, up to 10 × 11 cm. Lobes irregular, imbricate, 2–9 mm wide, often irregularly wrinkled, with margins ± sinuate, entire to dentate, frequently lobulate, eciliate ( Fig. 23C ). Upper surface greenish grey, pale or ± darkened, usually somewhat shiny, faintly to clearly punctiform white-maculate, smooth to rugose, sometimes slightly scrobiculate, often cracked in older parts, isidiate, lacking schizidia, pustules, dactyls, soralia. Isidia sparse to dense, at times obscuring the thallus surface, marginal and laminal, mostly on the central lobes ( Fig. 23C ), eciliate, coralloid-branched, rarely inflated or lobulate, apices concolor or brownish, up to 2 mm high. Lobules frequent, marginal, isidiate or not, up to 5 × 5 mm. Medulla white throughout. Lower surface rugulose or granulate, sometimes reticulate near lobe tips, ± shiny, black to the margin, or with a buff, ivory, or chestnut brown erhizinate marginal zone (ca. 1–3 mm wide) at main lobe tips. Rhizines in ± scattered clusters, when marginal some rhizines can be seen from above and thereby resemble cilia; concolor to the lower surface, simple, sometimes furcate, up to 1 mm long. Apothecia found on the holotype, up to 6 mm in diameter, disc imperforate, margin crenate, very early coralloid-isidiate ( Fig. 23D ). Ascospores 19.5– 22.4 –25 × 10– 11.2 –12 µm, Q = 1.75– 2.01 –2.27(2.30), epispore (1.5)– 2.0 –(2.5) µm thick, n = 30, from 1 thallus. Pycnidia rare, submarginal towards the lobe apices; only primordia seen. Conidia not found.

Chemistry:— Spot tests and fluorescence: upper cortex K+ yellow, UV−; medulla K−, C+ and KC+ rose to red, P−, UV−. Secondary metabolites (TLC): upper cortex with atranorin and chloroatranorin; medulla with evernic acid (major) and lecanoric acid (minor).

Geographical distribution:— So far only known with certainty from Réunion and Mauritius, where it seems to be rare. The first collection (lectotype) was made in Réunion in the Cirque de Mafate by frère Rodriguez (= Émile Athanase Marquet) in 1889. Since then, Parmotrema meiospermum has only been found on this island at two other localities in two UTM 1× 1 km grid cells (or two UTM 2× 2 km grid cells, Fig. 23A ), at two very different elevations: 120 and 1370 m.

Dodge (1959) reported the species from Mauritius and Rodrigues in the Mascarenes, Madagascar, Anjouan ( Comoros) and Tanzania. However, there are some doubts about these records, at least part of the cited material belongs to the widespread P. tinctorum ( Hale 1965a: 262) . Nevertheless, P. meiospermum is present in Mauritius, as attested to by a specimen collected by Krog and Timdal in 1991 which we examined.

Ecology:—The lectotype was most probably saxicolous, but the recent Reunionese specimens were found on bark of a living tree and a dead shrub. The Mauritian specimen was also corticolous. The ecology of the species is rather difficult to summarize, the only three recent known occurrences being quite dissimilar. In Réunion, one is located in a disturbed lowland rainforest, under a pluvial tropical bioclimate with a lower thermotropical thermotype belt (It = 645) and a lower hyperhumid ombrotype belt (Io = 13.8); the other is located in a disturbed leeward montane rainforest, under a pluvial tropical bioclimate with a lower mesotropical thermotype belt (It = 407) and an upper humid ombrotype belt (Io = 9.9) ( Fig. 23B ). In Mauritius, the site is located in a disturbed lowland rainforest, at 600 m elevation. In the current state of knowledge, it seems difficult to reconcile the apparent rarity of this lichen with its ecological niche, which appears to be quite broad.

Notes:— Parmotrema meiospermum is the only species of the genus whose medulla contains the orcinol depside evernic acid.Although placed in the subdivision Amphigymnia of the genus Parmelia by Hue (1899) and Dodge (1959), this taxon was not treated in the Hale’s monograph ( Hale 1965a), probably owing to its unusual medullary chemistry ( Hale examined the type collection in 1962, according to the enclosed label). Later on, Hale (1974c) included it in Pseudoparmelia Lynge , but with some doubt ( Hale 1976). Finally, he synonymized it with Hypotrachyna bogotensis (Vain.) Hale ( Hale & DePriest 1999) , an American species that is also isidiate and shares the same extrolites ( Sipman et al. 2009).

Our phylogenetic study, using a three loci data matrix, shows that this taxon does belong to the genus Parmotrema , in which it forms a well supported clade, together with P. mascarenense and P. aurantioreagens ( Fig. 3 ).

Specimens examined:— FRANCE. Réunion: Cilaos , southern side of le Bonnet Carré, GR R1 trail, elev. 1370 m, 21°07’36”S, 55°28’04”E, in disturbed leeward montane rainforest, in an overall S orientation, on bark of the trunk of an undetermined dead shrub, 18 August 2015, D. Masson 974.4717 (LG); Saint-Philippe, Basse Vallée, route forestière 36, elev. 120 m, 21°22’08”S, 55°42’27”E, on the edge of a road through a disturbed lowland rainforest, in an overall S orientation, on bark of the trunk of an undetermined tree, 15 August 2015, D. Masson 974.4648 (LG) .

MAURITIUS. Black River District: along the path from Plaine Champagne towards Piton de la Petite Rivière Noire, elev. 600 m, corticolous, 05 November 1991, H. Krog & E. Timdal (O L-21226) .

Figures

FIGURE 3. Phylogeny of the Parmotrema species studied. Best ML tree resulted from a RaxML analysis of three loci (EF1-α, ITS, mtSSU) and 102 specimens. Punctelia toxodes was selected as the outgroup. Bootstrap values are represented above the branches, and thick branches have bootstrap support value ≥ 70. Results of the species delimitation analyses are summarized to the right of the terminal labels of the tree. The first column corresponds to the results of the Stacey analysis, while the second column corresponds to the results of the bPP analysis. Specimens attributed the same colour were reconstructed as part of the same putative species by the species delimitation analysis. Major medullary extrolites are also shown for each specimen.

FIGURE 23. Parmotrema meiospermum. 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: Gross morphology of thallus (Masson 974.4648); D: Apothecia with coralloid-isidiate margin (holotype). Scale bars: A = 10 km; C = 10 mm; D = 4 mm.