## 1 Introduction  
License (also known as lichenized fungi [1]) are symbiont organisms between fungi and algae/cyanobacteria [2]. They could be considered a potential source of new drugs [3] due to their bioactive secondary metabolites with various pharmacological effects [4]. One of the most significant representatives in the lichens world is the _Ulsnea_ genus (_Parmiaceae_, lichenized _Ascomycetes_), a potent phytomedicine with various pharmacological activities [5]. It has more than 600 species, endemic to Asia, Africa, Europe, and America and is used worldwide for traditional medicines (except in Australia) and food preparation [6]. _Ulsnea_ sp. can be transplanted for air monitoring [7], and, at the same time, their culture conditions could be optimized, aiming for biomass increasing and antioxidant metabolite production [8]. Due to their significant diversity, the _Ulsnea_ lichens are mainly studied in various Earth regions: Europe [9], India [10], Russia [11], Taiwan [12], Turkey [13], and New Zealand [14]. _U. barbata_ is a valuable representative of the _Ulsnea_ genus, used in ethnomedicine, homeopathy, and the cosmetic industry [15]. Moreover, [PERSON] et al. [16] proved that _U. barbata_ was used as human food (mush and lichen bread) for survival in four-year-long (1992-1995) war conditions in Bosnia. All _U. barbata_ benefits are due to its chemical composition, which is strongly dependent on growth conditions [17]. [PERSON] et al. [18] quantified in _U. barbata_ various primary and secondary metabolites. The most well-known phenolic secondary metabolites reported are oligosaccharides, monosaccharides (glucose and galactose), citric, succinic, alpha-linolenic, and stearic acids. According to [PERSON] et al. [19], various polyhydroxylated lipids, fatty acids, and other undetected compounds can be added to the _U. barbata_ phytochemical profile. The fungal partner (mycobiont) synthesizes these specific compounds mainly due to symbiosis. As a response to biological and abiotic stress, the secondary metabolites are extracellular and are found within the lichen thalli as crystals on the fungal hyphae surface [20]. The primary metabolites are required for lichen growth and nutrition. They are intracellular in fungal or algal (photobiont) cells [20]. By weight, the mycobiont predominates in _U. barbata_, compared to photobionts, assuring the form of the thallus built due to both symbiotic partners' activity. _U. barbata_ is a fruitclose lichen; its thallus has a heteromerous structure with three layers: cortex, medulla, and central axis (central cord). As a cover, _U. barbata_ has a thin cortex (external layer) with a subcortical, low represented algal zone. These structures are followed by a medulla and a cartilaginous central axis (central cord) [9]. The upper cortex has a compact structure formed by a dense pack of fungal hyphae, with a protective role. Algal cells interweaved with fungal hyphae compose the green algal zone [9]. The medulla is thick and loose, with rare fungal hyphae. Finally, the central axis (central cord) is formed by longitudinal fungal hyphae that are densely packed, forming a compact cartilaginous structure [21]. Around this central cord, the other layers (medulla and cortex) and algal zone have a radial disposition. Both associated organisms function in the symbiotic process. The algal partner provides carbohydrates resulting from photosynthesis; they are directly transferred to the lichen-forming fungus in a specific form, thus increasing the resistance to desiccation [22]. The mycobiont assures the nutrients and metals required for algal metabolic processes. Moreover, the fungal partner synthesizes secondary metabolites to protect the photobiont against extreme temperatures, UV exposure, desiccation, and herbivores [23]. When a high heavy metal accumulation in the lichen thallus occurs, these lichen metabolites form complexes, increasing lichen metal tolerance [24]. When heavy metals pass intracellularly, they are expected to influence the lichen metabolic processes.