Parmotrema mellissii (C.W. Dodge) Hale (1974a: 337) MycoBank no. 343083

Parmelia mellissii C.W. Dodge (1959: 134) MycoBank no. 368691

Type:— UNITED KINGDOM. Saint Helena [without locality], s.d., J. C. Melliss 23 (BM, n.v., holotype, fide Hale 1965a; US [image!], isotype).

(Fig. 24)

Thallus foliose, loosely to moderately adnate, membranaceous to subcoriaceous, up to 11 × 15 cm. Lobes rounded, imbricate, irregularly branched, 4–10 mm wide, often concave; margins ascending, crenate to isidiate, ciliate (Fig. 24C). Cilia conspicuous, black, often with coppery glints (pigments), abundant, simple, up to 4.5 mm long. Upper surface pale greenish grey, emaculate or faintly white-maculate, somewhat scrobiculate, ± reticulated cracked in the older parts, isidiate, sorediate or sorediate-isidiate. True soralia sometimes develop submarginally by disintegration of the upper cortex, but they soon turn into ± ciliate isidiomorphs; isidia marginal and submarginal, rarely laminal, often ciliate, developing into ± coralloid-branched isidioid outgrowths, up to 4 mm high, and soon becoming sorediate (Fig. 24D). Soredia granulose, (50)– 59.2 –(75) µm in diameter (n = 60, from two specimens, SD = 7.6 µm). Medulla white, occasionally orange-pigmented in decaying parts. Lower surface shiny, smooth to rugulose, black, rhizinate, with a shiny, erhizinate marginal zone (ca. 1–3 mm wide), chestnut brown, but mottled with ivory white at the isidiate lobes. Rhizines black, irregularly distributed, simple, rarely furcate, long (up to 2 mm). Apothecia absent. Pycnidia rare, submarginal, black. Conidia bacilliform, 6–8 × ca. 1 µm.

Chemistry:— Spot tests and fluorescence: upper cortex K+ yellow, UV−; medulla K−, C−, KC + fleeting purple pink, P−, UV+ blue-white; pigmented medulla K+ purple. Secondary metabolites (TLC): upper cortex with atranorin and chloroatranorin; medulla with alectoronic and α-collatolic acids and skyrin (in the pigmented medulla); 3 undetermined ciliary pigments: PV constant, ± O2, ± BG.

Geographical distribution:—Pantropical species that extends into some warm-temperate areas in both hemispheres (Hale 1965a, Louwhoff 2001, Kurokawa 2006). In the MIOI hotspot, it has been reported from Madagascar (Aptroot 1990) and from Réunion (van den Boom et al. 2011). On the later island it appears to be a rare species, only found at two localities (in two UTM 1× 1 km grid cells, or two UTM 2× 2 km grid cells, Fig. 24A), with similar elevations (1740 and 1760 m), in the Piton des Neiges massif.

Ecology:—On Réunion, Parmotrema mellissii was found on bark, sometimes overgrowing mosses, of two endemic species: the tree Acacia heterophylla and the tree heather Erica reunionensis. Two habitats are concerned, natural Acacia montane forest, with undergrowth grazed extensively by livestock, and Erica montane thicket, along a crest at the top of cliff. Bioclimate features of the two localities are similar (Fig. 24B): bioclimate = pluvial tropical, thermotype belt = upper mesotropical (It = 330 and 395), ombrotype belt = lower hyperhumid (Io = 16.7 and 17.2). The ecology of P. mellissii in Réunion resembles that of this species in eastern Tanzania (Krog 2000) where thalli were found between 1300 and 2400 m elevation, in montane and submontane rainforests, elfin forest, as well as ericaceous heath. In Madagascar, a cloud forest at 1800 m elevation hosted this species (Aptroot 1990). Elsewhere, P. mellissii also occurs in drier habitats (e.g. Louwhoff & Elix 2002) and can be saxicolous (e.g. Bungartz & Spielmann 2019).

Notes:—The morphological variability of vegetative reproductive structures within the same thallus, as well as between different thalli, is noteworthy in the material examined. This variability, which has already been highlighted by several others (e.g. Divakar & Upreti 2005, Marcelli & Benatti 2011, Egan et al. 2016), raises the question of the possible taxonomic heterogeneity of the specimens. All Reunionese samples examined have true isidia, at least at juvenile stages, which generally become sorediate more or less rapidly. One specimen also has true soralia, without cilia, originating from the breakdown of the submarginal upper cortex, which subsequently develop into more or less ciliate isidiomorphs. The species with the most similar phenotype, Parmotrema hypomiltoides (Vainio) Kurok., is distinguished by the absence of true isidia and by a medulla distinctly pigmented red-orange by euplectin (Hale 1965a, Kurokawa & Moon 1998, Louwhoff & Elix 1999).

Hale (1965a) reported that the cilia of P. mellissii sometimes react K+ purple and Marcelli & Benatti (2011) stated that this colour reaction was associated with the presence of a coppery pigmentation in some cilia. Our TLC investigations show that up to three pigments are involved, two of which (O2, BG) were found, among the Parmotrema species from Réunion, in only one specimen of P. mellissii.

Despite the fact that P. mellissii is a fairly frequently discussed species in the literature, the characteristics of its conidia were so far only known from Brazilian specimens: bacilliform 6–7.5 × ca. 1 µm (Canêz 2005, Spielmann 2005), 5–7(8) × ca. 1 µm (Buril 2015). These data are in full agreement with those gathered in Réunion.

In our ITS tree, two accessions identified as P. mellissii from South America (GenBank accession no. ON312515 and ON312513, the latter under the name P. paulense — see below Specimens studied for comparison) were recovered close to the one from Réunion, however the relationship between the three was not resolved (Fig. 4). In our 3-locus phylogenetic analysis, the two species P. mellissii and P. mirum D.M. Masson & Sérus. sp. nov. were resolved as a supported entity, and both produce alectoronic acid as a major medullary extrolite (Fig. 3).

Specimens examined: — FRANCE. Réunion: La Possession, cirque de Mafate, plaine des Tamarins, elev. 1760 m, 21°04’44”S, 55°26’37”E, in Acacia montane forest, on bark of A. heterophylla, 27 July 2005, D. Masson 974.1768 (Hb. DM); ibid., on mossy bark of branch of A. heterophylla, 22 August 2017, D. Masson 974.5070 (LG); Salazie, Bélouve, elev. 1740 m, 21°04’40”S, 55°31’41”E, in Erica montane thicket, on bark of Erica reunionensis, 25 August 2013, D. Masson 974.4480 (Hb. DM).

Specimens studied for comparison:— COLOMBIA. Antioquia: Medellín, ParqueArví, 06°16’49”N, 75°30’00”W, elev. 2449 m, by track into forest, on fallen twig, 03 November 2014, D.L. Hawksworth s.n. (MAF-Lich 20060) [cited by Stelate et al. (2022) as Parmotrema paulense].

CUBA. Loma San Juan, elev. 900 m, July 1932, B. Hioram 10302 (REN 000035).

DOMINICAN REPUBLIC. Cordillera Central, in gap on main ridge between Pico del Yaque and L. Chinguela, elev. ca. 2150 m, elfin woodland type of mist forest with scattered pines, 10 August 1958, C. M. Wetmore 3735 (REN 000037).

JAMAICA. High Peak, Blue Mountains, 14 March 1953, H.A. Imshaug 15225 (REN 0000036).

MEXICO. Chiapas: Lagos de Monte Bello near the Mexico-Guatemala border, about 50 km southeast of Comitán, elev. 1220 m, mature pine forest, on conifers, 25 March 1960, M.E. Hale & T.R. Söderstrom 20961 (REN 000053).