Unearthing a fungal giant: Dianjunaceae fam. nov., a novel Paleocene lineage of Xylariales harboring Dianjunus rex gen. et sp. nov

During mycological surveys in Yunnan Province, China, specimens of a fungus producing massive, upright stromata up to 50 cm high and individually 2.2 kg in weight were sampled. Through an integrative taxonomic approach combining detailed morphology, multilocus phylogeny [internal transcribed spacer (ITS), large subunit ribosomal DNA (LSU), RNA polymerase II subunit 2 ( RPB2) , and beta-tubulin ( TUB2) ], and phylogenomic analyses, this fungus is proposed as the new species Dianjunus rex gen. et sp. nov., the type of the new family Dianjunaceae ( Xylariales ). Phylogenetic analyses robustly place Dianjunaceae as a distinct sister clade to Graphostromataceae . Divergence time estimation dates the origin of this family to the early Paleocene (~65 million years ago), coinciding with the period following the Cretaceous–Paleogene (K–Pg) extinction, when an estimated 75% of all plant and animal species went extinct, and a significant ecological reorganization of life on Earth happened. The stromata of D. rex represent the largest fructifications documented within the Ascomycota , significantly expanding the known morphological range of the Xylariales . The study provides a comprehensive description, including a nodulisporium-like anamorph with periconiella-like branching patterns, and discusses the taxon’s phylogenetic placement and distinctive morphology. This discovery highlights the unexplored fungal diversity in East Asian forests.