Scientific names are crucial for communicating knowledge concerning fungi and fungus-like organisms. In plant pathology, they link information regarding biology, host range, distribution and potential risk to agriculture and food security. In the past, delimitation among pathogenic taxa was primarily based on morphological characteristics. Due to distinct species sharing overlapping characteristics, the morphological identification of species is often neither straightforward nor reliable. Hence, the phylogenetic species concept based on molecular phylogenetic reconstructions gained importance. The present opinion discusses what a fungal species is and how identification of species in plant pathology has changed over the past decades. In this context, host-specialization and species complexes are discussed. Furthermore, species concepts in plant pathology are examined using case studies from Bipolaris, Colletotrichum, Curvularia, Diaporthe, Diplodia, Meliola, Plasmopara, rust fungi and Trichoderma. Each entry contains a brief introduction to the genus, concepts used in species identification so far and the problems in describing a species followed by recommendations. The importance of correctly naming and identifying a species is addressed in the context of recent introductions, and we also discuss whether the introduction of new species in pathogenic genera has been overestimated. We also provide guidelines to be considered when introducing a new species in a plant pathogenic genus.

This study documents the morphology and phylogeny of micro-fungi collected from various medicinal plants in southern China and northern Thailand. Based on morphological characteristics and phylogenetic analyses, 99 species were identified, classified within one phylum (Ascomycota), spanning three classes (Dothideomycetes, Leotiomycetes and Sordariomycetes), 16 orders, 36 families and 67 genera. We introduce one new order, Oncopodiellales, two new families, Catenuliconidiaceae and Oncopodiellaceae, one new genus, Biascospora, and 48 new species: Achroiostachys brunnea, A. catenata, Amphisphaeria hibiscicola, Apiculospora thailandensis, Arecophila maolanensis, A. yunnanensis, Barriopsis caryotae, Biascospora chishuiensis, Conioscypha synnemata, Diaporthe ervatamiae, D. kunmingensis, D. tuchungicola, Dictyocheirospora xishuiensis, Diplocladiella hainanensis, Distoseptispora gelatinosa, D. olivaceoviridis, Gregatothecium diflugossae, Helicosporium multiseptatum, Helminthosporium thailandicum, Kalmusia tetrastigmae, Keissleriella yunnanensis, Lasiodiplodia houttuyniae, L. liliacearum, Leptospora houttuyniae, Lophiotrema asexuale, L. guizhouense, Melanopsamma tongrenensis, Memnoniella chiangmaiensis, Murichromolaenicola dendrobii, Heleiosa brunnea, Neohelicascus guizhouensis, Neohelicomyces sexualis, Neohendersonia tongrenensis, Neomassaria fibraureae, Neoscytalidium dendrobii, Parabahusutrabeeja hyalina, Paramyrothecium xishuiense, Phaeosphaeria boehmeriae, P. guiyangensis, Phaeosphaeriopsis oblongispora, Psiloglonium bambusicola, P. brunneum, P. guizhouense, Roussoella panzhouensis, Seriascoma guizhouense, Striaticonidium olivaceobrunneum, Vamsapriya chiangraiensis and Virgatospora thailandica, with illustrations, discussions of their taxonomic placement, and comparisons with morphologically similar taxa. Twelve new combinations are introduced: Conioscypha chiangmaiensis (≡ Vanakripa chiangmaiensis), C. minutiellipsoidea (≡ Vanakripa minutiellipsoidea), Conioscypha obovoidea (≡ Vanakripa obovoidea), Heleiosa guizhouensis (≡ Neoheleiosa guizhouensis), H. lincangensis (≡ Neoheleiosa lincangensis), Keissleriella acaciae (≡ Pleurophoma acaciae), K. italicum (≡ Pleurophoma italica), K. ossicula (≡ Pleurophoma ossicola), K. pleurospora (≡ Phoma pleurospora), Phaeosphaeria brachylaenae (≡ Didymocyrtis brachylaenae), P. pini (≡ Didymocyrtis pini) and P. septata (≡ Didymocyrtis septata). Additionally, we report 34 new host records from medicinal plants and seven new geographical records for China and Thailand. We also resolved inter-generic synonymy for two species. A reference specimen is designated for Diplocladiella taurina. Detailed descriptions and illustrations of all these taxa are provided.

Bamboo is a widespread plant with medicinal value. During our taxonomic study on medicinal plants, three collections of Distoseptispora were made from China and Thailand. Phylogenetic analyses of combined LSU, ITS and RPB2 sequence data showed that two collections represented a new species, phylogenetically distinct from other described species in Distoseptispora. This new species has macronematous, mononematous conidiophores, polyblastic or monoblastic conidiogenous cells and acrogenous, solitary, straight, obclavate, multi-septate, thick-walled conidia. Distoseptispora bambusae sp. nov. is introduced with illustrations and a comprehensive description. The third collection on dead wood from Thailand was identified as D. tectona with newly-generated molecular data for this taxon.

A Kirschsteiniothelia species was found on decayed twigs of Ficus microcarpa collected at the Garden of Medicinal Plants in Chiang Rai, Thailand. Phylogenetic analyses of combined ITS, LSU and SSU sequence data showed the new isolate was phylogenetically distinct from other known species of Kirschsteiniothelia. Accordingly, Kirschsteiniothelia thailandica sp. nov. is described and illustrated and compared with other species in the genus.

Phylogenetic analyses of combined LSU, rpb2, tub2 and ITS sequence data of representative Xylariales taxa indicated that Diabolocovidia, Didymobotryum and Vamsapriya cluster together and form a distinct clade in Xylariales. Morphological comparison also shows their distinctiveness from other families of Xylariales. Therefore, we introduce it as a novel family, Vamsapriyaceae. Based on morphological characteristics, Podosporium and Tretophragmia, which were previously classified in Ascomycota genera incertae sedis, are now included in the Vamsapriyaceae. In addition, three Vamsapriya species, V. chiangmaiensis sp. nov, V. uniseptata sp. nov, and V. indica are described and illustrated in this paper.

Four stains were isolated from two fresh twigs of Helwingia himalaica and two dead woods during investigations of micro-fungi in China and Thailand. Phylogenetic analyses of four gene regions LSU, ITS, SSU and tef1-α revealed the placement of these species in Montagnula. Based on the morphological examination and molecular data, two new species, M. aquatica and M. guiyangensis, and a known species M. donacina are described. Descriptions and illustrations of the new collections and a key to the Montagnula species are provided. Montagnula chromolaenicola, M. puerensis, M. saikhuensis, and M. thailandica are discussed and synonymized under M. donacina.