Parmotrema cetratum (Ach.) Hale (1974a: 335) 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 : 28-29

Parmotrema cetratum (Ach.) Hale (1974a: 335) MycoBank no. 343018

Parmelia cetrata Ach. (1814: 198) MycoBank no. 373825

Type:— USA. Pennsylvania, s.d., G.H.E. Muhlenberg s.n. (H, n.v., lectotype designated by Hale & Fletcher 1990; UPS, n.v., isolectotype) .

≡ Rimelia cetrata (Ach.) Hale & A. Flechter (1990: 26) MycoBank no. 102561

( Fig. 11 )

Thallus foliose, loosely adnate, membranaceous, 11 × 10 cm ( Fig. 11C ). Lobes irregular, contiguous to imbricate, irregularly branched, 3–6 mm wide, ± rounded axils, round to subtruncate apices; margins dentate to laciniate, ciliate ( Fig. 11D ). Cilia black, numerous, marginal, simple or squarrose, rarely irregularly branched, up to 2 mm long. Upper surface pale greenish grey, reticulate (occasionally effigurate) white-maculate, ± finely reticulate cracked along the maculae; lacking soredia, isidia, schizidia, pustules, dactyls and phyllidia. Laciniae common, especially in the central part, marginal, flat or slightly canaliculate, ± dichotomously branched, up to 15 mm long, 1–2.5 mm wide, ciliate. Lobules absent. Medulla white throughout. Lower surface punctate, ± shiny, duller in the central part, black to the margin, or with a chestnut brown marginal zone (ca. 1–2.5 mm wide) at main lobe tips. Rhizines black, numerous, ± evenly distributed, often extending to lobe margins, simple or squarrose, up to 3 mm long. Apothecia scarce, immature, laminal, stipitate, up to 2 mm in diameter, disc perforate, margin slightly crenate, amphithecium smooth. Ascospores absent. Pycnidia rare, laminal on some laciniae, black. Conidia not found (11 pycnidia investigated).

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 acid (major) and consalazinic acid (minor).

Geographical distribution:—A tropical and subtropical species extending in some temperate areas. It is known from North (e.g. Brodo et al. 2001, Egan et al. 2016), Central (e.g. Holz & Gradstein 2005, Rosabal et al. 2012), and South (e.g. Marcano et al. 1996, Benatti & Marcelli 2008, Flakus et al. 2011) America, Eastern and Southern Africa (e.g. Krog & Swinscow 1981, Hale & Fletcher 1990), Asia (e.g. Kurokawa & Lai 2001, Aptroot & Feijen 2002, Jayalal et al. 2013, Bawingan et al. 2017), and Oceania (e.g. Elix 1994; Louwhoff & Elix 1999, 2002; Moon et al. 2001; Galloway 2007). In the MIOI hotspot, it is only cited from Madagascar ( Hue 1899, des Abbayes 1961, Aptroot 1991). On Réunion Island, it is an apparently rare species collected only once in a single place on the northern flank of the Piton des Neiges, at an elevation of 800 m in the Cirque de Salazie ( Fig. 11A ).

Ecology:—Examination of the only specimen from Réunion preserved in an herbarium shows that it grew on organic matter, probably on a rocky substrate. The bioclimate of the locality ( Fig. 11B ) is pluvial tropical in the lower mesotropical belt (It = 482) and the lower hyperhumid ombrotype belt (Io = 13.0). Unfortunately, no other ecological data are available.

In Madagascar, P. cetratum is both corticolous and saxicolous. It was recorded from sea level (mangrove) to 1800 m (cloud forest) ( des Abbayes 1961, Aptroot 1991). A similar elevational range was found in the Hawaiian Islands ( Moon et al. 2001).

Notes:—The specimen from Réunion can be assigned to P. cetratum owing to its reticulate maculate upper surface, the presence of marginal cilia and laciniae, simple or squarrose rhizines extending to the margin of the lobes, the lack of vegetative propagules, and the presence of salazinic and consalazinic acids in the medulla. The delimitation of this species remains problematic, however, as there is no agreement amongst authors on the diagnostic phenotypic characters. As an example, several taxa placed in synonymy by Hale & Fletcher (1990) were recognized as good species by Spielman & Marcelli (2020). The first available molecular data (Divakar et al. 2005) also suggest that the morphological characteristics of this taxon need to be reassessed.

Specimen examined:— FRANCE. Réunion: Salazie, von Îlet à Vidot zum Rivière du Mât und Grand Sable , elev. 800 m, 21°03’S, 55°30’E, Erdanrisse, Basaltfelsen und freistehende Bäume, 17 August 1991, K. & A. Kalb 33714 ( WIS) .

Figures

FIGURE 11. Parmotrema cetratum. A: Distribution on Réunion (UTM 2×2 km grid system); B: Bioclimatic characteristics of collection site (abbreviations and threshold values for thermotype and ombrotype horizons from Rivas-Martínez et al. 2011: 17–18); C: Gross morphology of thallus (Kalb & Kalb 33714); D: Laciniate and ciliate lobes, with ± reticulate white-maculate upper surface (K. & A. Kalb 33714). Scale bars:A = 10 km; C = 10 mm; D = 4 mm.