Jahnula purpurea J.Fourn., Raja & Shearer, a new species in the Jahnulales (Dothideomycetes) collected from submerged wood in a freshwater river in Martinique Island, Lesser Antilles, is described and illustrated. The characteristic features of the new species are: globose to subglobose, brownish black ascomata with broad, golden brown, subtending hyphae which stain the underlying wood purple; a peridial wall composed of large pseudoparenchymatic cells, which are textura angularis to prismatica in surface view; sparsely septate pseudoparaphyses embedded in a gel matrix; clavate to obclavate asci with a short pedicel; brown, one-septate, ellipsoidal, rough-walled ascospores without a gelatinous sheath or appendages. Unfortunately, because limited material was available from the type collection, we were unable to obtain molecular data. Jahnula purpurea is distinct from all previously described species of Jahnula in its ability to stain the wood purple and in a combination of ascomal, ascus, and ascospore size and morphology.

Aquatic fungi, Lotic, Submerged wood, Systematics, Morphology

The genus Jahnula, typified by Jahnula aquatica (Plöttner and Kirschst.) Kirschst., is the largest genus in the Jahnulales, Dothideomycetes and currently contains 15 species (Hyde 1993; Hawksworth 1984; Hyde and Wong 1999; Pinruan et al. 2002; Raja and Shearer 2006; Raja et al. 2008; Sivichai and Boonyuen 2010; Suetrong et al. 2011). All species of Jahnula have been reported from submerged decorticated wood in freshwater habitats, mostly from tropical/subtropical habitats. Exceptions are J. aquatica, J. apiospora A. Carter, Raja & Shearer, and J. sangamonensis Shearer & Raja, which have been described and reported from fresh water in temperate geographical locations (Hawksworth 1984; Raja and Shearer 2006; Raja et al. 2008). Members of the Jahnulales are primarily reported from freshwater habitats, except Manglicola guatemalensis Kohlm. & E. Kohlm, that is a mangrove species (Suetrong et al. 2010).

In this paper, we describe and illustrate a new species of Jahnula that was found on submerged wood collected from a freshwater river on Martinique Island, Lesser Antilles.

The methods for collection, morphological characterization and illustration are outlined in Fournier and Lechat (2010) and Réblová et al. (2015). Asci and hamathecia were mounted in black ink (Pelikan brand) for illustrations. Culturing was attempted, but without success. Since the fungus has been collected only from the type locality thus far and limited material was available to serve as a holotype specimen, attempts made to extract DNA and obtain molecular data from a very small number of ascomata were also unsuccessful. The holotype specimen is deposited in the Illinois Natural History Survey Fungarium (ILLS).

Jahnula purpurea differs from all other species of Jahnula in that it stains the wood on which it grows purple. In addition, it is one of the species of Jahnula, which has minute ascomata (125–185 µm diameter). The only other species reported to have minute ascomata is Jahnula marakotii Sivichai & Boonyeun, a species reported from a submerged wood test block of Azadirachta indica from a peat swamp in Thailand (Sivichai and Boonyeun 2010). Jahnula purpurea differs from J. marakotii in a number of morphological characters such as shape and size of asci and ascospores. The asci of J. purpurea are clavate to obclavate (90–98 × 22.5–25 µm), while those of J. marakotii are cylindrical (107.5–120 × 9–11.5 µm). The ascospores of J. purpurea do not possess apical appendages and are larger in size (24–28 × 8–9 µm), while those of J. markotii are equipped with bipolar, hyaline apical appendages and are shorter (17.5–20 × 5–6.5) in size.

Jahnula purpurea should also be compared to the type species of the genus, J. aquatica, in that the ascospores of the two species look morphologically similar at first glance. The two species are however, quite distinct. Jahnula purpurea has smaller ascomata, clavate asci, and smaller ascospores, while J. aquatica has larger ascomata, cylindrical asci, and larger ascospores (Hawksworth 1984; Hyde and Wong 1999; Raja and Shearer 2006). In addition, J. purpurea stains its wood substrate purple (Fig. 1A–C), which has never been reported for substrates on which J. aquatica occurs (Hawksworth 1984; Raja and Shearer 2006). Another species of Jahnula that is morphologically similar to J. purpurea in overall ascomata and ascospore morphology includes J. australiensis. On closer examination, however, the species are quite distinct. Jahnula purpurea stains subtending wood purple, a character not observed in J. australiensis; the asci in J. purpurea are clavate to obclavate, while those of J. australiensis are cylindrical; the ascospores of both the species are some what similar in size (24–28 × 8–9 µm in J. purpurea vs. 19–30 × 6–8 µm in J. australiensis) but those of J. purpurea are slightly smaller and wider.

Several species of freshwater ascomycetes in the family Amniculicolaceae are capable of staining underlying wood substrates purple (Zhang et al. 2009a; Zhang et al. 2009b; Zhang et al. 2012), a characteristic similar to J. purpurea. However, Amniculicolaceae is phylogenetically related to the Pleosporales, while based on morphological data presented herein J. purpurea belongs to the Jahnulales (Pang et al. 2002; Campbell et al. 2007; Suetrong et al. 2011).

In addition, species of Massariosphaeria such as M. phaeospora (E. Müll.) Crivelli has the ability to stain wood purple (Zhang et al. 2012). Lophiostoma purpurascens (K.D. Hyde & Aptroot) Aptroot & K.D. Hyde reported from submerged wood in freshwater habitats in Australia and Papua New Guinea also stains wood purple (Hyde and Aptroot 1998; Hyde et al. 2002). However M. phaeospora, and L. purpurascens are phylogenetically unrelated to the Amniculicolaceae (Zhang et al. 2012). Another recently described species, Massariosphaeria fridae M. Spooren stains its substrate (dead stalks of Alisma plantago-aquatica) red (Spooren 2007). This suggests that unrelated freshwater Dothideomycetes have the ability to stain the vicinity of their substrate red or purple. It would be interesting to study the secondary metabolites from these taxa in the future to understand if there is an underlying ecological significance to the production of bright pigments by species of both terrestrial and freshwater ascomycetes within the Dothideomycetes. Additional collections and molecular sequence data from J. purpurea in the future would certainly shed light on the hypothesis of purple pigment being a true phylogenetic informative character at the family-level within the Dothideomycetes as suggested by Zhang et al. (2012). The production of purple pigment on wood by J. purpurea suggests that pigment production might be a case of convergent evolution that could be functionally significant within the Dothideomycetes. It is also likely that different colors might be characteristic of different phylogenetic clades and might have similar or dissimilar ecological functions.

HAR would like to thank Dr. Nicholas H. Oberlies, UNCG for logistics provided to complete this manuscript. We also thank the reviewers for their valuable comments.