Rust fungi (Pucciniales, Basidiomycota) of the Brazilian Cerrado: Taxonomic advances and new taxa in a threatened biome

The Brazilian savanna designated as Cerrado is one of the most biodiverse biomes in the world, yet it has lost nearly 50% of its native vegetation since the mid-20th century, mostly due to agricultural expansion. This rapid degradation makes it one of the most threatened biodiversity hot spots worldwide, highlighting the urgent need for intensified conservation and biodiversity research efforts. The systematic study of rust fungi (Pucciniales) in the Brazilian Cerrado began around 140 years ago with the temporary emigration from Germany of the explorer and collector Ernst Heinrich Georg Ule (*1854–†1915) to Brazil where he was hired as a “visiting naturalist” serving in the National Museum of Rio de Janeiro from 1891 until 1895. Since then, approximately 270 species of rust fungi have been documented in the Cerrado. Historically, taxonomic classifications of rust fungi relied strongly on the interpretation of morphological traits, which are prone to subjective bias that has led to taxonomic instability and is reflected in complex taxonomic histories. Furthermore, recent molecular phylogenetic studies have revealed a high frequency of homoplasious traits in rust fungal morphology, further complicating accurate taxonomic decisions when such traits are considered in isolation. In this study, we conducted morphological and molecular phylogenetic analyses on several rarely collected and studied genera of Cerrado rust fungi, evaluating phylogenetic relationships and discussing their taxonomy. We describe a new Puccinia species infecting the genus Coracoralina (Eriocaulaceae: Poales), Puccinia coracoralinae, sp. nov. along with a new genus Dietelomyces, gen. nov. and several new combinations, i.e. Cerradopsora pouteriae, nom. nov. Dietelomyces copaiferae, comb. nov. besides defining the suprageneric status of Esalque holwayi, Dietelia duguetiae, Kimuramyces cerradensis, and Mimema venturae. Additionally, we discuss the effects of identified homoplasious traits on rust fungal systematics based on our phylogenetic analyses. Considering published estimates of rust fungal diversity in other regions, we conclude that with approximately 12 356 documented vascular plant species in the Cerrado, at least ca. 2300 rust fungal species can be expected to be present. This suggests that, to date, ca. of 13% of the rust fungi occurring in the Cerrado has been documented. Given the alarming threat status of the Cerrado and its extremely significant biodiversity, we also emphasize and discuss the potential implications of systematic rust fungal research for future conservation policies in this unique ecosystem. By addressing key taxonomic and phylogenetic gaps, this study highlights rust fungi as a critically understudied component of Cerrado biodiversity and reinforces the urgent need to expand field collections and integrate fungal systematics with conservation strategies as habitat loss accelerates.