## 1 Introduction
According to archival data from 1948 on wild food plants used in Poland, fruits were the most frequently gathered part of plants. The fruits were commonly consumed raw--especially by children as snacks--or processed into preserves. Among the most frequently collected fruits, lingonberry ranked 7 th, while blackthorn, elderberry, and hawthorn are listed among the top 20 species [12]. The medicinal use of elderberry, lingonberry, and rowanberry is also mentioned in the paper concerning the folk culture of the Polish-Lithuanian-Belarusian borderland from the early 20 th century [13]. Despite the health-related properties of chokeberry, its crop and usage spread in Poland relatively late, in the 20 th century [5]. Fruits contain huge amounts of polyphenols, which are considered potent scavengers of free radicals and reactive oxygen species. Several studies have indicated that a high content of polyphenols corresponds to a high antioxidant capacity [14]. Among polyphenols, flavonoids are known to confer numerous health benefits in mammalian systems; thus, they act as antimicrobials, stimulate the production of antibodies, and exhibit hypotensive and anticancer effects due to their antioxidant properties [9]. Phenolic acids are involved in mechanisms of defense against biotic and abiotic stresses and may exhibit anticancer, antiinflammatory, and antimicrobial potential [15]. The antioxidant properties of flavonoids and phenolic acids are associated with the presence of aromatic rings and free hydroxyl (-OH) groups in the structure [16]. Ellagic acid (EA, dilatone of hexahydroylphenic acid) and quercetin (Q, 3,3,4,5,7-pentahydroylflavone) belong to the most well-known polyphenols--phenolic acids and flavonoids/flavonols, respectively. In plants, ellagic acid can occur in the free form (EA) or as conjugates with various sugars (EACs, glycosylated form), as well as polymeric ellagitannins (ETs) (hydrolysable tannins) from which it can be released upon hydrolysis [17]. Raspberries, strawberries, and pomergranates are well-recognized sources of EA and are available as dietary supplements. Quercetin is predominantly found in plants as glycosides (e.g., quercetinarabinosides in berries), while its aglycone form occurs less frequently [18]. EA and Q exhibit antiglycative functions, thereby reducing harmful effects associated with the formation of advanced glycation end products (AGEs) [16]. The ability to metabolize xenobiotics [19], hepatoprotective effects [20], and promising evidence about anticancer activity [21] of these polyphenols have also been reported. However, it should be highlighted that Q, at high concentrations, may exhibit mutagenic effects [22]. The purpose of this study was to verify whether fruits of Polish wild medicinal plants with known therapeutic uses can serve as good dietary sources of EA and Q. Taking into account both their popularity and medicinal/pharmaceutical properties, the following fruits were selected for this study: barberry, blackthorn/sloe, chokeberry, elderberry, hawthorn, lingenberry, rowanberry, and sea-buckthorn. In selecting these fruits, particular attention was given to species with a broad geographical distribution, ensuring their relevance not only within Poland but also across a significant part of Europe. Currently, little information is available on EA and Q content in these fruits. The determination of EA and Q in plant extracts was carried out using ultra-high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS).