## 1 Introduction  
Regions with a history of auriferous mining activities are regarded as extreme ecological environments, predominantly due to the deleterious ecological ramifications that arise from these anthropogenic disturbances. The processes involved in gold extraction are responsible for the release and accumulation of heightened concentrations of heavy metals and metalloids, which can lead to environmental contamination and present a myriad of health hazards to humans [1, 2, 3]. The elevated levels of arsenic, along with other metals and metalloids in these areas, can impose selective pressures that favor the survival of distinct, resistant and well-adapted fungal species [4]. Nevertheless, mycological investigations within these environments have been pointed as being limited [4], and further research on the fungal biodiversity, resistance traits and genomic characteristics in such settings, still needs to be thoroughly studied and documented. The Fungal Kingdom comprises a vastly diverse collection of eukaryotic organisms, showcasing a broad range of morphological, ecological and metabolic traits that enables them to thrive in diverse environments across the planet. Owing to their distinctive features, fungi are recognized for their broad spectrum of biotechnological applications and valued for their sociological, ecological and economic significance [5; 6; 7; 8]. The genus _Penicillium_ represents one of the most globally prevalent fungal genera, inhabiting a wide array of ecosystems, including terrestrial substrates, vegetation, air, indoor spaces and a variety of alimentary products [9; 10; 11]. A substantial proportion of _Penicillium_ species function as ubiquitous saprophytes, readily located in nearly any ecological niche [9]. They exhibit remarkable adaptability to diverse physical and chemical environments, which encompass a range of water activity (aW), pH, thermal gradients, environmental contaminants and redox potential variations. In addition, arsenic resistance within the genus has been documented, leading to its identification as integrant inhabitants of mining soil mycobiomes [4; 12]. Owing to their metabolic capacities, _Penicillia_ species have been reported as relevant microorganisms for the bioremediation of contaminated habitats, due to the ability of some species to tolerate and \"remove\" uranium, cadmium, lead and arsenic from the environment [13; 14; 15; 16; 4; 17]. In addition, acid-tolerant and metal-resistant _Penicillia_ are known to be key players in extreme environments, contributing to geochemical cycles and organic matter breakdown [16]. Moreover, some _Penicillium_ species have been reported as holding some additional biotechnological interesting properties due to, for instance, their abilities for intra and extracellular biosynthesis of gold nanoparticles, which can have applications in the pharmaceutical and biomedical fields [18; 19]. In an effort to contribute to the knowledge of abandoned gold mining areas microbial biodiversity, we have recently applied Next-Generation-Sequencing (NGS) methods to study the microorganisms thriving in the abandoned and flooded Portuguese Escadia Grande gold mine (Gois, Portugal) [20]. Moreover, in an attempt to shed light on the hidden fungal diversity in this area, we conducted a survey of culturable fungal species from soil/rocky materials from the mine interior. We have continuously isolated various specimens belonging to a _Penicillium_ species during this investigation. The aim of this work was to determine the taxonomic position of this species, by employing a polyphasic approach consisting of phylogenetic analyses (\(\beta\)- tubulin (_BenA_), Internal Transcribed Spacer region (ITS rDNA), calmodulin (_CaM_) and the RNA polymerase II subunit 2 (_rbp2_)), coupled with morphological and ecological considerations. This analysis highlighted these isolates' identity as _Penicillium mexicanum_ and allowed us to document some unreported morphological traits for this species.