Parmotrema crossotum 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 : 42-44

Parmotrema crossotum D.M. Masson & Sérus. , sp. nov. MycoBank no. 853867

Diagnosis. Characterized by the dentate to incised lobe margins with long and dense cilia containing two K+ pigments, the upper surface not distinctly maculate, the polymorphic esorediate isidia, often long-ciliate, ± branched, sometimes ± flattened, long and very brittle, the bacilliform to weakly sublageniform conidia, 6–8 µm long, and the presence of alectoronic acid as the only medullary extrolite detectable by TLC.

Holotype:— FRANCE. Réunion: Saint-Louis, Les Makes, Bois Bon Accueil , elev. 1180 m, 21°11’31”S, 55°23’57”E, in leeward montane rainforest, in an overall south orientation, on bark of Agauria salicifolia , 28 August 2017, D. Masson 974.5155 (MNHN-PC-PC0088070; isotype: LG).

GenBank accession numbers: ITS ( PP 840471), EF1-α ( PP 852845).

( Fig. 17 )

Thallus foliose, loosely to moderately adnate, membranaceous, up to 12 × 20 cm. Lobes irregular, imbricate, 3– 12 mm wide, irregularly wrinkled, often ± concave, apices ± rounded, with margins undulated, crenate, dentate to incised, occasionally lobulate, ciliate ( Fig. 17E ). Cilia black, some with coppery glint; conspicuous, dense and ± evenly distributed at the lobe margins (2–3 cilia per mm of margin), also present on isidia and isidioid outgrowths, sometimes laminal; simple, rarely 1–2 times branched, slender, ca. 0.03–0.07 mm in diameter at the base, up to 7 mm long on lobe margins, up to 5.5 mm long on isidia. Upper surface pale greenish grey, rather dull, somewhat shinier towards lobe tips, smooth to rugose, emaculate or faintly white-maculate, sometimes slightly cracked in older parts; isidiate, lacking schizidia, pustules, dactyls, soralia. Isidia ± abundant, mainly marginal, ± extending submarginally with age, occasionally also laminal, in particular at the apex of conical protuberances; highly variable in shape and size, irregularly cylindrical, simple to ± coralloid branched, sometimes flattening irregularly and then resembling narrow branched laciniae, or forming ‘moose or fallow deer antlers’ like structures; very frequently with long lateral (more rarely apical) cilia; up to 6 mm high (excluding cilia), very brittle ( Fig. 17C & 17D ). Lobules rare, marginal, up to 1 × 1 mm. Medulla white throughout, rarely tinged with yellow (K−) in decaying parts. Lower surface rugulose, rarely smooth, ± shiny, black to the margin, or with a chestnut brown, or tan, erhizinate marginal zone (ca. 2–8 mm wide) at main lobe tips, sometimes mottled with ivory white in a narrow (0.4–1 mm) marginal zone at the isidiate lobes. Rhizines in ± scattered groups, concolor to the lower surface, polymorphic, mostly simple, but up to 3 times branched, slender to stout, 0.04–0.2 mm in diameter, up to 4 mm long. Apothecia absent. Pycnidia quite frequent, submarginal on lobes, also on isidia, black. Conidia bacilliform to weakly sublageniform, 6–8 × ca. 1 µm. Upper cortex palisade plectenchymatous, not fragile, (23)– 26.5 –(30) µm thick. Algal layer ± continuous, (13)– 19.8 –(25) µm thick. Medulla (113)– 147.9 –(162) µm thick. Lower cortex prosoplectenchymatous, (20)– 26.2– (30) µm thick.

Chemistry:— Spot tests and fluorescence: upper cortex K+ yellow, UV−; medulla K−, C−, KC + fleeting purple pink, then orange, P−, UV+ blue-white. Secondary metabolites ( TLC): upper cortex with atranorin and chloroatranorin; medulla with alectoronic acid (major); ± 2 undetermined ciliary pigments: P1 and PV.

Etymology: — From the Greek krossotos: fringed. The specific epithet refers to the presence of long and numerous cilia at the margin of the lobes.

Geographical distribution:—So far only known from Réunion. It seems to be a rare species, having been collected in only three localities in three UTM 1× 1 km grid cells (or three UTM 2× 2 km grid cells, Fig. 17A ). These localities are distributed at elevations between 1180 and 1335 m in the northwestern part of the island, in the Piton des Neiges massif.

Ecology:— Parmotrema crossotum is a corticolous species, found on trunks and branches of the native Agauria salicifolia (Lam.) Hook. and Weinmannia sp. , as well as the introduced Psidium cattleianum . Leeward and windward montane rainforests are the two habitats reported. The bioclimate of the localities is pluvial tropical; thermotype belt is lower mesotropical (445 ≤ It ≤ 480), ombrotype belts are more variable = from lower humid to lower hyperhumid (8.2 ≤ Io ≤ 15.0) ( Fig. 17B ).

Notes:—This species is superficially similar to Parmotrema mellissii , with which it shares the pigmented cilia at the lobe margins, the upper surface not distinctly maculate, the frequently ciliate isidia, the bacilliform conidia 6–8 µm long, and the presence of alectoronic acid in the medulla. However, the cilia are less developed in P. mellissii , ciliary pigments are partly different, the upper cortex is fragile, soredia are produced in addition to the isidia, and α-collatolic acid occurs with alectoronic acid in the medulla. Molecular data further show that P. crossotum and P. mellissii are phylogenetically distinct ( Fig. 3 ).

Two other ciliate, emaculate Parmotrema with non-verrucose isidia, and containing atranorin in the upper cortex and alectoronic acid in the medulla can be confused with P. crossotum . The saxicolous and Neotropical P. erasmium (Hale) Hale is much less ciliate, the isidia are more uniform, shorter, thinner and never flattened, its medulla is distinctly pigmented with euplectin in the lower part ( Hale 1965a, Egan et al. 2016) and contains also an unidentified substance (± colourless, UV+ white; Rf classes:A4, C4–5) in addition to alectoronic acid (first author’s observation). The Asian and Australasian P. nanfongense (Kurok.) DePriest & B.W. Hale has also a more complex medullary chemistry with α-collatolic acid and 2–3 related compounds in addition to alectoronic acid, its marginal cilia are less dense and shorter, and its cylindrical isidia are shorter and more homogeneous in shape, with no tendency to flatten ( Kurokawa 1987, Louwhoff & Elix 1999, Wolseley et al. 2002; first author’s observation).

As demonstrated by phylogenetic analysis of a 3-locus dataset ( Fig. 3 ), P.crossotum belongs to a strongly supported radiation comprising ten species. Five of them could be endemic to Réunion (or the Mascarene Islands), three also occur on Madagascar, and two are more widespread in the Paleotropics.

Additional specimens examined (paratypes):— FRANCE. Réunion: La Possession, Dos d’Âne, Piton Grand Bazar , elev. 1335 m, 20°58’25”S, 55°23’26”E, in leeward montane rainforest, on bark of a trunk of Weinmannia sp. , 17 August 2012, D. Masson 974.3864 (Hb. DM); Sainte-Marie, Plaine des Fougères , between Ravine Sèche and Ravine Mère Canal, elev. 1325 m, 20°58’48”S, 55°30’47”E, in disturbed windward montane rainforest, in an overall NE orientation, on ± mossy bark of a branch of Psidium cattleianum , 30 August 2012, D. Masson 974.4130 ( LG) .

Specimens studied for comparison:

Parmotrema erasmium .— HONDURAS. Francisco Morazán: Quebrada El Gallo, northeastern slopes of Cerro de Uyuca , elev. 900 m, in pine-oak woods, 14 March 1951, C . V. Morton 7044 ( REN, paratype) .

Parmotrema nanfongense .— PAPUA NEW GUINEA. Central Province: Varirata National Park, on elevated conglomerate ridge 20 km E of Port Moresby, near the park buildings, elev. 800 m, 9°27’S, 147°22’E, epiphyte on scattered trees in parkland, 19 March 1987, H. Sipman 22.371 (B); ibid., ca. 22 km E of Port Moresby, near Varirata Lookout, elev. 800 m, 9°26’S, 147°21’E, dry secondary forest with Casuarina and Eucalyptus and conglomerate rock outcrops, 23 October 1995, H. Sipman 38669 (B).

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 17. Parmotrema crossotum. 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 & D: Isidiate lobes with irregularly cylindrical or ± flattened, simple to ± branched, highly ciliate isidia (C: holotype, D: Masson 974.4130); E: Gross morphology of thallus (holotype). Scale bars: A = 10 km; C, D = 4 mm; E = 10 mm.