Parmotrema occultum 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 : 77-80

Parmotrema occultum D.M. Masson & Sérus. , sp. nov. MycoBank no. 853875

Diagnosis. Similar to Parmotrema crinitum , but differs by the thicker cupular exciple and by its ITS barcode ( Table 3).

Holotype:— FRANCE. Réunion: Saint-Benoît, Bébour , piste forestière 3 de Takamaka, elev. 1240 m, 21°05’59”S, 55°34’44”E, in windward montane rainforest, on bark of branch of Dombeya sp. , 16 August 2017, D. Masson 974.4966 (MNHN-PC-PC0088078).

GenBank accession numbers: ITS ( PP 840530), mtSSU ( PP 842604), EF1-α ( PP 852872).

( Fig. 30 )

Thallus foliose, moderately adnate, membranaceous to subcoriaceous, up to 16 × 19 cm. Lobes irregularly branched, imbricate, 5–11 mm wide, irregularly wrinkled; margins sinuate, crenate to dentate, irregularly isidiate, at times shortly laciniate or lobulate, ciliate ( Fig. 30E ). Cilia black, sparse to moderately dense, unevenly distributed at the margin of the lobes and lobules, also present on isidia, slender, mostly simple, rarely 1–2 times branched or slightly squarrose, ca. 0.03–0.05 mm in diameter at the base, up to 1.8 mm long. Upper surface pale greenish grey, shiny at the periphery, duller towards the centre, ± clearly white-maculate, ± rugose, occasionally a little cracked in the older parts, isidiate, lacking soralia, schizidia, pustules, dactyls. Isidia sparse to dense, marginal and laminal, but often more concentrated submarginally, cylindrical to coralloid, occasionally irregularly flattened; often laterally and/or apically ciliate; up to 2.5 mm high ( Fig. 30D ). Laciniae rare, marginal, poorly developed, unbranched to slightly branched, up to 1 mm long, 0.2–0.5 mm wide, ciliate, at times isidiate. Lobules occasional, marginal, up to 6 × 9 mm, ciliate. Medulla white throughout. Lower surface smooth, rugulose or granulate, shiny towards the lobe tips, duller in the central parts, black to the margin, or with a chestnut brown, erhizinate or partly rhizinate, marginal zone (ca. 1–4 mm wide) at main lobe tips, lateral lobes with isidia occasionally with a narrow erhizinate, buff or buff-mottled, marginal zone (0.2–1 mm wide). Rhizines numerous, ± evenly distributed, black, slender, mostly simple, rarely 1–2 times branched or squarrose, up to 3 mm long. Apothecia present in the holotype, submarginal, cupuliform, ± flattening with age, up to 8 mm in diameter, stipitate on constricted stipes (up to 1.3 mm in diameter); disc imperforate, orange-brown, concave, initially shiny and smooth, then ± rough and dull; margin crenate, with ± branched and ciliate isidia; amphithecium rugose, white-maculate, not or weakly isidiate; hymenium s. lat. (80)– 114.8 –(150) µm high, proper exciple with hyaline layer (8)– 12.3 –(17) µm high, intermediate layer (10)– 16.2 –(25) µm high, cortex-like basal layer (32)– 39.7 –(45) µm high. Ascospores 8 per ascus, simple, colourless, broadly ellipsoidal to ellipsoidal, (22)23– 27.6 –32 × 12– 14.7 –17(18) µm, Q = (1.57)– 1.88 –2.22(2.31), epispore (3)– 3.5 –(4) µm thick, n = 30, from one thallus. Pycnidia rare, submarginal, black. Conidia bacilliform 5.5–7.5 × ca. 1 µm. Upper cortex palisade plectenchymatous, (15)– 19.0 –(25) µm thick. Algal layer here and there briefly interrupted, (15)– 20.3 –(27) µm thick. Medulla (110)– 136.7 –(163) µm thick. Lower cortex prosoplectenchymatous, (15)– 18.5– (20) µm thick.

Chemistry:— Spot tests and fluorescence: upper cortex K+ yellow, UV−; medulla K+ yellow, C−, KC−, P+ orange, UV−. Secondary metabolites ( TLC): upper cortex with atranorin and chloroatranorin; medulla with stictic acid (major), constictic acid (minor), menegazziaic acid (trace), cryptostictic acid (trace) and hypostictic acid (trace).

Etymology:—From the Latin occultus: hidden, concealed. The new taxon is phenotypically very similar to Parmotrema crinitum and was confused with it before molecular analysis.

Geographical distribution:—Currently known only from two localities on the windward side of the Réunion Island ( Fig. 30A ), at relatively low elevations (1085 and 1240 m).

Ecology:—The two collected specimens were found in cloud forests (windward montane rainforest and Pandanus montane wet thicket), one on the bark of a branch of Dombeya sp. , the other on the mossy bark of a trunk of Pandanus montanus . Parmotrema occultum appears to be an ombrophilous species and somewhat more thermophilous than its close relative P. crinitum , as suggested by the bioclimatic indices (bioclimate pluvial tropical) of the two collection localities: thermotype belts = upper thermotropical (It = 500) and lower mesotropical (It = 415), ombrotype belts = upper hyperhumid (Io = 20.8) and ultrahyperhumid (Io = 29.2) ( Fig. 30B ). We did not collect P. crinitum at the same locations where P. occultum was found, and it would be very interesting to precisely compare the ecological niches of these two lichens, for example in the Forêt de Bébour where both were found, but at different elevations: 1240 m for P. occultum , 1390, 1405 and 1520 m for P. crinitum .

Notes:—Molecular investigations of Reunionese Parmotrema with ciliate lobe margins, commonly ciliate isidia, black lower surface, and unpigmented medulla with stictic and constictic acids as main secondary metabolites revealed the existence of two distinct lineages ( Fig. 3 & 4 ). One is most likely P. crinitum (see the entry for this taxon). The other relates to a very similar taxon overall, but a posteriori comparative analysis of specimens from both lineages suggests the existence of subtle differences. Compared to P. crinitum , the near-cryptic taxon tends to have wider lobes (5–11 vs 2–9 mm), and the isidiate lateral lobes less frequently have an erhizinate margin on the underside and, when it occurs, it is narrower and buff rather than ivory-white. The average thickness of the cupular proper exciple is an interesting anatomical diagnostic feature, as it is distinctly thicker in P. occultum ( Fig. 15A , Fig. 30C ). However, these potential phenotypic differences need to be confirmed by examining more thalli, particularly those of P. occultum . We found no differences in the relative thickness of the three layers of the proper exciple (Fisher’s exact test, two-tailed, P = 0.795), or in the size and shape of the ascospores or conidia ( Table 6), or in the secondary chemistry (at least with the resolution capacity of TLC).

Hale (1965a) and Hale & DePriest (1999) listed seven species-level names as heterotypic synonyms of P. crinitum . Parmelia proboscidea Taylor , Parmelia excrescens (Arnold) Zopf (based on Imbricaria perlata var. excrescens Arnold ), and Parmelia pilosella Hue were described from European material ( Taylor 1836, Arnold 1882, Hue 1898). Our phylogenetic tree based on ITS sequences ( Fig. 4 ) shows that European specimens from France, Norway, mainland Portugal, and Switzerland nest together with North American specimens, and part of the Reunionese material, in the same Parmotrema crinitum-P. perlatum clade ( Stelate et al. 2022). So, it is unlikely that the names Parmelia excrescens , P. pilosella and P. proboscidea would apply to our near-cryptic taxon. This is also the case with Parmelia schweinfurthii Müll. Arg. , described from the island of Socotra, Yemen ( Müller 1882). A specimen from this island, whose ITS has been studied (GenBank accession AY251442), seems to be more closely related to Parmotrema crinitum than our near-cryptic taxon ( Fig. 4 ). Parmelia pseudocatharinensis Gyeln. is based on P. catharinensis Müll. Arg. f. isidiosa Müll. Arg. , from Brazil ( Müller 1891). The type material in G is accompanied by two annotation labels by M. Hale . One, typed, is dated 1959 and indicates ‘ Parmelia crinita Ach. [probably]. Atranorine, stictic acid +’. The other, handwritten and dated 1974, mentions ‘ Parmelia internexa Nyl. TLC : stictic, norlobaridone, atranorin, constictic’. The occurrence of norlobaridone in addition to stictic acid and related substances, as well as the non-ciliated isidia (cf. photograph of type material from G; cilia not cited in the protologue) are indeed characteristic of Parmotrema internexum ( Spielmann & Marcelli 2009, Lendemer 2015). Parmelia catharinensis f. isidiosa is therefore a junior synonym of Parmotrema internexum , and not of P. crinitum as indicated by Hale (1965a) and Hale & DePriest (1999). The enigmatic Parmelia tuckermanii Du Rietz , from Cuba, has non-ciliate isidia and produces small ascospores (7–9 × 14–17 µm), with a thin epispore (ca. 1 µm) ( Du Rietz 1924). It is therefore quite different from our near-cryptic taxon, and even its synonymy with Parmotrema crinitum is questionable. It is much the same for Parmelia chlorocarpa Müll. Arg. , described from Venezuela. Philippe Clerc kindly examined for us the type in G. Norlobaridone was not detected by TLC and the lobe margins are copiously ciliate. However the isidia are eciliate, and the average thickness of the cupular exciple is more similar to those found in Parmotrema crinitum from Réunion than to those of our near-cryptic taxon. As we have not found any existing species-level name that could match the near-cryptic species related to P. crinitum , we describe it as new.

In our 3-locus analysis, the four species P. crinitum , P. nephophilum , P. occultum and P. perlatum were resolved as a single supported clade ( Fig. 3 ). The sibling species P. occultum was resolved with strong support on a distant branch, and recognized as a distinct species by both Stacey and bPP analyses.

Additional specimen examined (paratype):— FRANCE. Réunion: Saint-Philippe, forêt de Saint-Philippe, sentier de Piton Ravine Basse Vallée, elev. 1085 m, 21°19’28”S, 55°42’16”E, in Pandanus montane wet thicket, in an overall SSW orientation, on ± mossy bark of a trunk of Pandanus montanus , 16 August 2013, D. Masson 974.4269 (LG).

Nomenclatural comment:—The status of species rank for Imbricaria perlata var. excrescens Arnold needs further comments. Hale & DePriest (1999) as well as Mycobank (www.mycobank.org, accessed 21 November 2022) stated Parmelia excrescens (Arnold) Hav. The combination P. excrescens was indeed used by Havaas (1918) in his work reporting the presence of Parmotrema crinitum in Norway. However, Index Fungorum (www.indexfungorum. org, accessed 21 November 2022) proposes Parmelia excrescens (Arnold) Zopf , according to an earlier publication ( Engler & Prantl 1907: 34). Indeed, the new combination already appears in a paper by Zopf published in 1897 ( Zopf 1897: 280).

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 15. A: Comparison of the average thickness (± SE) of the cupular exciple of mature apothecia of 10 specimens of P. crinitum and one specimen of P. occultum. Means and standard errors were calculated from 5–12 measurements taken on a mature apothecium from each specimen of P. crinitum, and on two different mature apothecia from the same thallus of P. occultum (Masson 974.4966); B: Scatter plot of mean ascospore width versus mean ascospore length for 10 specimens of P. crinitum, two of which were also genetically analysed. For each sample, 30 randomly selected ascospores from a single well-developed apothecium were measured.

FIGURE 30. Parmotrema occultum. 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: Transverse sections of mature apothecia of P. crinitum (left, Masson 974.5107) and P. occultum (right, holotype), stained in lactic cotton blue, showing the cupulate proper exciple clearly thicker in P. occultum; D: Isidiate lobe with ciliate, simple to coralloid-branched isidia (Masson 974.4269); E: Gross morphology of thallus (holotype). Scale bars: A = 10 km; C = 100 µm; D = 3 mm; E = 10 mm.