Unveiling species diversity within early-diverging fungi from China I: three new species of Backusella (Backusellaceae, Mucoromycota).

The species diversity of early-diverging fungi has long lagged behind that of higher fungi, posing a significant obstacle to our comprehensive understanding of the fungal kingdom. Our ongoing research endeavors aim to address this gap by exploring the species diversity of early-diverging fungi in China. In this study, we describe three novel species within the Backusella, namely B.elliptica sp. nov., B.fujianensis sp. nov., and B.variispora sp. nov., based on phylogenetic and morphological analyses. In the phylogenetic analysis of the ITS (internal transcribed spacer), LSU (large subunit of ribosomal RNA gene), and RPB1 (RNA polymerase II largest subunit gene) regions, the B.elliptica and B.fujianensis cluster closely with B.gigacellularis, B.ovalispora, and B.solicola, and the B.variispora is closely related to B.locustae and B.pernambucensis. Morphologically, B.elliptica is distinguished by elliptical sporangiospores, as well as cylindrical and hemispherical columellae. The B.fujianensis is characterized by elliptical sporangiospores, and various types of columellae such as hemispherical, subglobose, depressed globose and conical. The B.variispora is characterized by subglobose to globose sporangiospores, as well as hemispherical, subglobose to globose columellae. Additionally, the sporangiophores are long and monopodially branched in B.elliptica and B.fujianensis, while short and simple or sympodially branched in B.variispora. Physiologically, the maximum growth temperatures of B.elliptica (32 °C), B.fujianensis (35 °C), and B.variispora were (35 °C) were determined. With the inclusion of these newly described taxa, the total number of Backusella species known from China now stands at 12. Finally, we provide a key to facilitate the morphological identification of Backusella species from Asia.