Nigromargarita tarda gen. et sp. nov. and distribution of an intron position class within Pleosporales

<i>Pleosporales</i>, the largest order in <i>Dothideomycetes</i>, has a broad host range and inhabits host plants as epiphytes, endophytes, parasites and saprophytes. <i>Trematosphaeriaceae</i> is a monophyletic family in <i>Pleosporales</i>, composed of species of deviated ecological background and morphological traits. In this study, we described a new fungal taxon under <i>Trematosphaeriaceae</i>, based on root endophytic fungi recovered from the desert plant <i>Gymnocarposprzewalskii</i> in Gansu Province, China. The taxon is characterised by simple, aseptate conidia and pycnidia in unusually small sizes. Multilocus phylogenetic analysis, based on ITS, LSU, SSU and TEF sequences and a morphology study indicated that the taxon represented a new genus within the <i>Trematosphaeriaceae</i> and was named <i>Nigromargaritatarda</i>. Intriguingly, an intron of 355 bp in length located at site 453 on the ribosomal SSU gene was detected in one strain of <i>N.tarda</i>. Sequence analysis and phylogenetic analysis indicated that the intron belongs to an intron position class (Pcl) restricted to <i>Pleosporales</i>. Phylogeny affiliated distribution of this Pcl was confined at the genus or lower level, suggesting a horizontal transmission pattern of this Pcl. This study established a new genus in <i>Trematosphaeriaceae</i> and depicted the spread features of a less-documented Pcl amongst <i>Pleosporales</i> families with high resolution, which promotes our understanding of the origin and transmission mechanism of such mobile genetic elements.