Morphological, molecular and 3D synchrotron X-ray tomographic characterizations of <i>Helicascus satunensis</i> sp. nov., a novel mangrove fungus

A new species of <i>Helicascus satunensis</i> sp. nov. was collected on mature dead fruits of the <i>Nypa</i> palm in Satun Province, southern Thailand. Its morphological characteristics are similar to those of the genus <i>Helicascus</i>. Recently, a genus <i>Helicascus</i> with three species from marine habitats worldwide was studied. The morphology of this fungus was investigated and combined with multigene sequence analyzes of small subunit (SSU), large subunit (LSU), internal transcribed spacer (ITS) ribosomal DNA, translation elongation factor 1-alpha (TEF-1<i>α</i>) and RNA polymerase II (RPB2) genes. Morphologically, <i>H. satunensis</i> sp. nov. is characterized by semi-immersed, lenticular ascomata, multilocules, a bitunicate ascus and smooth, obovoid, dark brown ascospores that are one-septate and unequally two-celled. In addition, 3D visualization using synchrotron X-ray tomography was performed to investigate the interaction between fruiting body and substrata. Molecular phylogeny with multigene revealed that <i>H. satunensis</i> sp. nov. belongs to the family Morosphaeriaceae, order Pleosporales, class Dothideomycetes. Furthermore, <i>H. satunensis</i> sp. nov. forms a well-supported clade with <i>Helicascus</i> species described from marine habitats. Based on the unique morphological and molecular evidence, we propose this fungus, <i>H. satunensis</i> sp. nov., as a new species for <i>Helicascus</i>.