Introduction
The genus Platythecium was introduced by Staiger (Reference Staiger2002) to accommodate species of Graphidaceae having a corticate thallus in various colours, a poorly developed lateral exciple but well-developed, flat lirellae, exposed discs and lacking distinct carbonization or with slight carbonization restricted to the base. Additional features characterizing the original nine species were colourless to brown submuriform, muriform or septate ascospores of small dimensions, not exceeding 20 µm in length.
Currently, Platythecium comprises 24 known species predominantly occurring on the bark of trees in tropical regions of Africa, America, Asia and Australia, with a large number of specimens also collected on tropical islands. Following the initial study of Staiger (Reference Staiger2002), the number of newly described or recombined species has been increasing steadily in subsequent years. Two further species of the genus were treated by Nakanishi et al. (Reference Nakanishi, Kashiwadani and Moon2003) and one was identified as incorrectly classified by Kalb et al. (Reference Kalb, Staiger and Elix2004). Three new species were later reported from India by Adawadkar & Makhija (Reference Adawadkar and Makhija2005) and one new representative of the genus by Makhija & Adawadkar (Reference Makhija and Adawadkar2005). Archer (Reference Archer2006, Reference Archer2007, 2009 Reference Archera , Reference Archerb ) contributed a comprehensive study on Australian Graphidaceae and added new palaeotropical species, including a key to the species on the Solomon Islands. Cáceres (Reference Cáceres2007) reported one new pantropical species from South America and Lendemer & Knudsen (Reference Lendemer and Knudsen2008) found an additional neotropical species from North America. The most recent species have been added by Cáceres et al. (Reference Cáceres, Aptroot, Parnmen and Lücking2014) in a study from South America and one new species from Sri Lanka was published by Weerakoon et al. (Reference Weerakoon, Lücking and Lumbsch.2014). Further information regarding the distribution of Platythecium species was provided by Lücking et al. (Reference Lücking, Johnston, Aptroot, Kraichak, Lendemer, Boonpragob, Cáceres, Ertz, Ferraro and Jia2014).
Material and Methods
Morphological and anatomical investigations were carried out using a Euromex Mic 1642 ZHT stereomicroscope and a Reichert Neovar compound microscope. The chemistry of the type specimens was observed by spot reactions with KOH, C, and Pd. All photographs for Figs 1 & 2 were taken using a Canon EOS 600D camera fitted with an LM-Scope camera adapter.
Platythecium seychellense (Stocker-Wörgötter LI 787329—holotype). A, thallus with branched apothecia up to 10 mm long; B, lirellae up to 4 mm long; C, section through apothecium, 0·2 mm wide, showing paraphyses with brown caps and hymenium (80 µm high). Scales: A & B=1 mm; C=0·1 mm.
Platythecium seychellense (holotype). A, asci (40–50×8–10 µm) with 8 ascospores; B, ascospores (8–12×4–5 µm), grey. Scales: A=20 µm; B=10 µm.
The specimens were collected in February 2015. The holotype has been deposited in LI and the isotypes in the private herbaria of the authors. One sample will be sent to Charles Morel, curator of the herbarium at the Seychelles Natural History Museum.
The New Species
Platythecium seychellense Neuwirth, Aptroot & Stocker-Wörgötter sp. nov.
MycoBank No.: MB 817223
Corticolous Platythecium with a smooth, shiny thallus, grey, 3-septate ascospores and paraphyses with brown caps. Ascospores 8 per ascus, 8–12×3–5 µm.
Type: Africa, Seychelles, Mahé, Morne Seychellois National Park, 4°39'00''S, 55°25'60''E, on bark of trees, 675 m, 6 February 2015, E. Stocker-Wörgötter (LI 787329—holotype; hb. Neuwirth 12327, hb. Stocker S 201, ABL—isotypes).
(Fig. 1)
Thallus crustose, corticate, grey-green, smooth, shiny.
Apothecia elongate, slender, partly branched, up to 10 mm long, 0·2–0·3 mm wide; disc flat, dark red-brown, margins entire (Fig. 1A & B); exciple not carbonized, sometimes with brown to orange hyphae. Hymenium hyaline, not inspersed, 75–80 µm high, KI−, I−; epithecium brown; hypothecium hyaline; paraphyses unbranched with brown caps (Fig. 1C); asci 40–50×8–10 µm. Ascospores 8 per ascus, grey, 3-septate, fusiform with rounded ends, I+ faintly blue, 8–12×3–5 µm (Fig. 2A & B).
Chemistry. No substances detected.
Etymology. The specific epithet refers to its only known locality on an island in the Seychelles.
Ecology and distribution. Mountain forest, on smooth bark of trees. The specimens were found close to the summit of Morne Blanc which is located within the Morne Seychellois National Park (Fig. 3). In the lower forest of Morne Blanc two typical higher plants of the Seychelles (Pandanus seychellarum and P. hornei) are present. Platythecium seychellense grows on smooth bark of trees higher up the mountain, which is covered by a nearly impenetrable misty rainforest of which Roscheria melanochaetes (endemic palm tree, Arecaceae) and Northia seychellana (‘Capucin’ tree, Sapotaceae) are important elements.
Tropical rainforest at summit of Morne Blanc, Mahé, 675 m.
Notes. The species is close to Platythecium albolabiatum but that species differs by the longer (12–15 µm) ascospores and whitish thalline margin. Platythecium leiogramma differs in having distinctly smaller lirellae (1–3×0·1–0·2 mm), and larger (9–13×5–7 µm) hyaline or pale brown ascospores. Platythecium grammitis is also similar to the new species but has hyaline ascospores, paraphyses with slightly yellow or orange-brown caps and pale yellow or brown discs.
Platythecium seychellense is the only species belonging to the genus that has so far been found on the Seychelles.
The curator of the University of Graz herbarium (GZU), Walter Obermayer, is thanked for providing some specimens of Platythecium for comparison. Specimens were collected using a research and collection permit from the Seychelles Bureau of Standards, issued by Elvis Nicette (managed by Katy Beaver, Conservation Action Group) and for providing the photograph used in Fig. 3.
