Parmotrema subisidiosum (Müll. Arg.) Hale (1974a: 339) MycoBank

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 : 107-109

Parmotrema subisidiosum (Müll. Arg.) Hale (1974a: 339) MycoBank no. 343134

Parmelia cetrata var. subisidiosa Müll. Arg. (1894: 256) MycoBank no. 373829

Type:— TANZANIA. Tanga: Usambara Mountains, Bumba, 1894, Holst 8772 p.p. (G [image!], lectotype; designated by Hale & Flechter 1990) .

≡ Parmelia subisidiosa (Müll. Arg.) C.W. Dodge (1959: 87) MycoBank no. 368820

≡ Rimelia subisidiosa (Müll. Arg.) Hale & A. Flechter (1990: 29) MycoBank no. 102570

( Fig. 40 )

Thallus foliose, loosely to moderately adnate, membranaceous to subcoriaceous, up to 11 × 12 cm. Lobes irregular, contiguous to imbricate, irregularly branched, 2–8 mm wide, often concave, rounded axils, round to subtruncate apices; margins often ascending, crenate to isidiate-dissected, sometimes shortly laciniate, ± ciliate ( Fig. 40C ). Cilia black, abundant to rare, mostly simple, occasionally squarrose, up to 2.5 mm long. Upper surface pale greenish grey, conspicuously reticulate white-maculate ( Fig. 40D ), ± finely reticulate cracked along the maculae, sometimes white-pruinose near lobe tips, isidiate, lacking schizidia, pustules, dactyls, phyllidia and soralia; regeneration lobules occasionally present in older parts. Isidia mainly marginal and submarginal, occasionally also laminal in older parts, sometimes shortly ciliate, ± cylindrical, generally soon branched and coralloid ( Fig. 40D ), occasionally becoming arbuscular with age; most 0.05–0.1 × 0.3–0.8 mm, but up to 3 mm high when arbuscular; apices often brownish. Medulla white throughout. Lower surface shiny near the margins, duller towards the centre, smooth to punctate, black and rhizinate to the margin, or with a narrow chestnut brown marginal zone (ca. 1–3.5 mm wide), rhizinate or not. Rhizines black, fairly dense in places, simple, squarrose, or irregularly branched, up to 2 mm long. Apothecia not seen in the specimens examined. Pycnidia rare, submarginal towards apices, black. Conidia bacilliform/filiform, 9–11 × ca. 1 µm.

Chemistry:— Spot tests and fluorescence: upper cortex K+ yellow, UV−; medulla K+ yellow then dark red, C−, P+ orange, UV−. Secondary metabolites (TLC): upper cortex with atranorin and chloroatranorin; medulla with salazinic (major) and consalazinic acids (minor).

Geographical distribution:— Parmotrema subisidiosum occurs on the Americas from 40° North to southern Uruguay ( Osorio 1983, Curtis 2017, Waters & Lendemer 2019, Spielmann & Marcelli 2020), as well as in the Galapagos ( Bungartz & Spielmann 2019), West Indies ( Imshaug 1957, Mercado-Díaz 2009) and Azores ( Arvidsson 1990, Purvis et al. 1993). It is also present in eastern and southern Africa ( Dodge 1959, Krog & Swinscow 1988, GBIF 2022c), Madagascar ( des Abbayes 1961, Aptroot 1990) and the Mascarene Islands of Réunion (van den Boom et al. 2011) and Mauritius (Diederich & Ertz 2020).

Hue (1899) was the first author to mention this taxon (as Parmelia cetrata var. subisidiosa Müll.Arg. ) on Réunion, from a corticolous specimen collected by Frère Rodriguez in 1889 in Salazie. Now, at least fifteen localities, in 14 UTM 1× 1 km grid cells (or 12 UTM 2× 2 km grid cells, Fig. 40A ), are known in Réunion to host this species. All but one are located in the leeward part of the island, mainly in the Piton des Neiges massif, between 910 and 1930 m elevation. This lichen seems to be most frequent inside and near the Cirque de Cilaos.

Ecology:—On Réunion, Parmotrema subisidiosum was found in submontane and montane rainforests, thriving on various substrates: bark (trees and branches), basaltic rocks, mosses (overgrowing bark or rock), or decaying wood. According to its elevational range (910–1930 m), the species appears to be moderately thermophilous. It is probably also mildly ombrophilous, on the basis of its predominantly leeward distribution on the island. The bioclimate of these leeward localities is pluvial tropical, with thermotype belts = from upper thermotropical to upper mesotropical (370 ≤ It ≤ 530) and ombrotype belts = from lower humid to lower hyperhumid (7.1 ≤ Io ≤ 13.0). The only windward location differs by its utrahyperhumid ombrotype belt (Io = 25.0) ( Fig. 40B ).

In East Africa, the species was collected in mountain massifs between 1500 and 3200 m elevation (Krog & Swinscow 1988, Krog 2000); the two Malagasy localities are located at 920 and 1800 m ( des Abbayes 1961, Aptroot 1990). In the mountains of Tanzania, where the type material comes from, P. subisidiosum has been found in natural habitats similar to those of Réunion (i.e. submontane and montane rainforests), but also in mossy elfin forest and Erica heath, as well as in some human-made habitats like tea plantation or edge of golf-course ( Krog 2000).

Notes:—The combination of an upper surface that is strongly reticulate maculate, the presence of true isidia, and a medulla with salazinic acid as major extrolite is characteristic of Parmotrema subisidiosum and the recently described P. saxoisidiatum Spielmann & Bungartz ( Bungartz & Spielmann 2019) . According to Bungartz & Spielmann (2019) and Spielmann & Marcelli (2020), P. saxoisidiatum is distinguished from P. subisidiosum by its less branched and non-ciliate isidia, and by its saxicolous ecology. We found a specimen from Réunion (No. 974.3860) with characters similar to those of P. saxoisidiosum . However, given the variability observed in the set of specimens from Réunion concerning the development of the isidia and the presence of cilia on them, as well as the diversity of substrates, we treated all of the collections from this island as P. subisidiosum . Parmotrema saxoisidiatum is so far only known from one collection from the Galapagos Islands and further data, including sequences, would be useful to test the relationship of this taxon with P. subisidiosum .

In our phylogenetic tree constructed from ITS sequences ( Fig. 4 ), the four specimens studied (three from Réunion, one from Mauritius) formed a well-supported monophyletic group. Parmotrema subisidiosum was recovered as sister to the P. reticulatum aggr. clade in our 3-locus analysis ( Fig. 3 ).

Specimens examined:— FRANCE. Réunion:Cilaos,above Îlet des Salazes,elev. 1820m, 21°06’26”S, 55°26’56”E, in leeward montane rainforest, on bark of a trunk of an undetermined shrub, 20 August 2012, D. Masson 974.3931 (Hb. DM); ibid., ca. 1 km W of Îlet des Salazes, trail GR R1-GR R2, elev. ca. 1750 m, in mesotherm rainforest, south-facing slope, 07 October 2003, U. Schiefelbein 1495 (B); ibid., Plaine des Fraises, elev. 1930 m, 21°06’50”S, 55°26’21”E, old Erica thicket in leeward montane rainforest, on bark of Erica reunionensis , 17 August 2015, D. Masson 974.4701 (Hb. DM); ibid., Bras Sec, sentier Kervéguen, elev. 1505 m, 21°07’42”S, 55°29’55”E, in leeward montane rainforest, on ± mossy bark of a trunk of an undetermined dead tree, 22 August 2012, D. Masson 974.3967 (Hb. DM); ibid., Bras Sec, western slope of Bonnet de Prêtre, elev. 1350 m, 21°09’03”S, 55°29’19”E, in leeward montane rainforest, on mosses on the WNW oriented and subvertical face of a small basalt rock, 21 August 2012, D. Masson 974.3962 (LG); ibid., Ravine des Calumets, elev. 1200 m, 21°09’20”S, 55°29’31”E, in secondary leeward montane rainforest, on ± mossy bark of a branch of an undetermined shrub, 21 August 2012, D. Masson 974.3948 (REU); ibid., sentier des Calumets, elev. 1075 m, 21°09’42”S, 55°29’23”E, in an anthropized wooded ravine, on a 62° inclined and WSW oriented face of a basalt rock, 21 August 2012, D. Masson 974.3957 (Hb. DM); Entre-Deux, la Grande Jument , elev. 1115 m, 21°12’46”S, 55°28’59”E, in leeward montane rainforest, on wood and decaying bark of a trunk of an undetermined dead tree, 16 August 2015, D. Masson 974.4665 (LG); ibid., sentier de la Grande Jument , elev. 910 m, 21°13’15”S, 55°28’53”E, in secondary leeward submontane rainforest with Psidium cattleianum , on bark of a trunk of an undetermined shrub, 16 August 2015, D. Masson 974.4660 (Hb. DM); La Plaine-des-Palmistes, Bras Noir, elev. 1220 m, 21°08.50’S, 55°35.20’, sheltered outcrop near stream, 26 May 2008, P. & B. van den Boom 39763 ( Hb. van den Boom); La Possession, Dos d’Âne, sentier des Lataniers, elev. 1140 m, 20°58’30”S, 55°23’31”E, in secondary leeward submontane rainforest with Psidium cattleianum , on the NW oriented and subvertical face of a basalt rock, 17 August 2012, D. Masson 974.3860 (Hb. DM); L’Étang-Salé, Chemin Canal, elev. 1075 m, 21°12’41”S, 55°22’36”E, in leeward submontane rainforest, on bark of a branch of Erica reunionensis , 27 August 2017, D. Masson 974.5141 (LG); Saint-Joseph, sentier du Piton du Rond, elev. 1140 m, 21°18’32”S, 55°36’04”E, in leeward submontane rainforest, on ± mossy bark of a trunk of a big Ficus tree, 18 August 2013, D. Masson 974.4294 (Hb. DM); ibid., Piton du Rond, elev. 1375 m, 21°17’55”S, 55°36’23”E, in leeward montane rainforest, on bark of a trunk of Molinea alternifolia , 18 August 2013, D. Masson 974.4311 (Hb. DM); Saint-Louis, Les Makes, Bois Bon Accueil, elev. 1185 m, 21°11’30”S, 55°23’56”E, in leeward montane rainforest, on bark of a branch of Dombeya sp. , 28 August 2017, D. Masson 974.5156 (Hb. DM).

MAURITIUS. Rivière Noire District: Black River Gorges National Park , along trail to Piton de la Petite Rivière Noire, elev. 630–700 m, 20.42133°S, 57.41947°E, on the bark of trees, 05 August 2016, P. Diederich 18464 (Hb. P. Diederich) .

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 4. Global tree (best scoring maximum likelihood tree) of Parmotrema based on the fungal ITS barcoding marker. Figure can be enlarged for a better reading of labels. Accessions in black are those retrieved from GenBank on June 2023. Those in red are those produced by the authors for this study. Bootstrap support is indicated on branch when ≥ 70%.

FIGURE 40. Parmotrema subisidiosum. 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 974.3962); D: Upper surface of isidiate lobe conspicuously reticulate white-maculate, and with cylindrical, ± coralloid-branched isidia (Masson 974.3931). Scale bars: A = 10 km; C = 8 mm; D = 2 mm.