Citizen survey maps exotic bolete’s expansion across Poland

A citizen-science ethnomycological survey documented the inland spread of the North American bolete Aureoboletus projectellus in Poland, confirming its presence in 60 of the country’s 380 counties and adding 56 localities that had not previously been reported. The study combined an anonymous online questionnaire with 112 face-to-face interviews near the Baltic coast, yielding 274 meaningful responses between 2019 and 2024. Its results show a distribution that continued expanding through 2023, while providing no statistical evidence that mushroom pickers were a principal vector carrying the fungus from the coast into new regions.

The species was first documented in Europe on the Curonian Spit in Lithuania in 2007, and an early Polish record was reported before 2011. Interview participants described collecting it in northern Poland in the late 1980s, but that claim is not supported by long-term monitoring of the region’s mycobiota. The researchers therefore treated 2007 as a potential starting point for the species’ expansion in Poland. Since then, its documented range has extended more than 600 km inland and encompasses almost all 16 Polish voivodships. The cumulative number of reports rose rapidly and was represented by both exponential and curvilinear functions, a pattern the authors interpret as consistent with an invasion curve moving from establishment into rapid expansion.

Most survey records came from Pomorskie, a Baltic coastal region containing the site of Poland’s earliest known occurrence near Sasino. In 205 of 274 cases, respondents said they had gathered the fungus there. Only 53% of the people collecting it in Pomorskie lived in that region; others were visitors who had travelled specifically to collect the species or tourists who encountered it while on holiday. The fungus is associated in Poland with pine woods containing heather. These concentrations of collecting activity at a major source area have turned A. projectellus into an ingredient of foraging tourism, in which visitors travel to known mushroom sites and gather the fungi themselves.

Following its initial discovery in Poland, the bolete was collected almost exclusively along the coast, but the distance between the original locality and later collection sites increased over time. Until 2016, all observations were confined to Pomorskie except for a single inland record in 2012. From 2017 onward, it began appearing at locations progressively farther from the Baltic source, particularly in southeastern Poland. The year 2023 produced the highest number of records, with increases in northern, central and southern Poland, including sites more than 500 km from the original introduction area. Because the cumulative curve had not plateaued, the authors considered the range to be still expanding. The curve describes reported occurrences, however, and is not a direct measurement of population size or abundance.

The questionnaire added 56 new Polish localities across 28 counties where the species had not previously been reported, with the new sites concentrated especially in southeastern Poland. A notable cluster occurred in the sandy lowlands of Podkarpackie, north and northeast of Rzeszów, where extensive pine forests are present. Some collectors in the region reported travelling between Lublin and Rzeszów to gather the fungus, and it was being sold at Rzeszów’s main vegetable market. Additional localities were reported around Warsaw, where pine forests coexist with a large population, and in Lubuskie, north of Lower Silesia. The species was not collected in southwestern Poland during the survey, and no records were reported from Podlaskie.

A. projectellus has also entered Polish food culture, and the researchers recorded 52 local names, 26 of which were used by at least two people. Names such as borowik amerykański, translated as “American bolete,” referred to the fungus’s geographic origin, while borowik wrzosowy, or “heather bolete,” described the heather-rich pine habitat in which it grows in Poland. Other commonly used names included amerykaniec, borowik wysmukły, amerykanin, złotak and złotoborowik wysmukły. Interview participants and mushroom collectors posting in social-media forums described the mushroom as tasty, fragrant and firm in texture. It was used similarly to other boletes, including in sauces, soups and pickles, and it was also dried for later use. Its culinary use had expanded to include Christmas Eve meals.

Preservation practices varied among the 269 respondents who answered the relevant question meaningfully. Drying and freezing were each reported by 61%, pickling by 44%, and consumption of fresh mushrooms after processing by 26%. Only one respondent mentioned salting for lacto-fermentation. The authors identify several features that may have helped the unfamiliar fungus gain acceptance. Its sponge-like undersurface places it within a group that Polish mushroom education commonly treats as relatively safe, while it lacks the bitterness that can make similar boletes undesirable. Its colour also resembles that of several popular edible species, including Boletus edulis, Suillus species, Imleria badia and Xerocomellus species. Once experienced mushroom pickers established that it was edible, the researchers suggest, it was quickly incorporated into a familiar folk grouping of edible boletes.

The research combined occurrence information from the literature, herbaria, the Global Biodiversity Information Facility and the researchers’ own field survey with active ethnomycological data collection. The researchers reduced spatial duplication by removing multiple species records within the same grid cell, retaining 325 occurrence records from 447 locations. The questionnaire and interviews then connected geographic occurrences with collectors’ origins, travel, local names, culinary practices and preservation methods. This active approach also gathered cultural information that was not available in the standard open-access occurrence repositories. Awareness of the mushroom’s exotic status was widespread among online respondents: 80% knew that the species was new and potentially invasive, whereas 19% did not.

The survey did not find a significant relationship between collectors’ place of origin and the number of records in a given region. Spearman’s rank correlation was −0.08, with p = 0.76, after Pomorskie was excluded because collectors deliberately travelled to that region. Some respondents from Śląskie and Dolnośląskie had collected the fungus in northern Poland, yet few localities were known in those regions. Conversely, numerous reports came from Podkarpackie, where the researchers encountered no people who had collected the fungus in northern Poland. These patterns provide no evidence that mushroom collectors were an important dispersal vector, although the study does not exclude their contribution alongside other mechanisms. Wind or animal vectors may be more influential, but the survey did not test those possibilities directly.

The ecological significance of the expansion remains uncertain because available data do not yet demonstrate whether A. projectellus harms native fungal communities. Under the strict IUCN definition, which requires a proven negative effect on native biota, the authors consider it better described for now as exotic rather than invasive. European Union rules also classify it as a novel food because it was not consumed in the union before 1997, complicating its legal marketing even though its sale was observed in Rzeszów. The researchers argue that decisions about promoting its edibility should depend on studies of its effects on native mycobiota, while the present evidence supports continued monitoring of its spread and use across Europe. The immediate picture is that a North American mushroom first documented in Europe in 2007 has become widely collected, named, eaten and reported across much of Poland, although both the causes of its inland spread and its ecological consequences remain unresolved.

Subject of Research: Citizen-science mapping of the spread, collection and culinary use of Aureoboletus projectellus in Poland

Article Title: Does a citizen science project describe the biogeography of exotic Aureoboletus projectellus in Poland? An ethnomycological survey

Article References: Pietras, M., Robak, D., Terlecka, M., & Łuczaj, Ł. (2025). Does a citizen science project describe the biogeography of exotic Aureoboletus projectellus in Poland? An ethnomycological survey. IMA Fungus, 16, Article e166407. https://doi.org/10.3897/imafungus.16.166407

Image Credits: AI Generated

DOI: 10.3897/imafungus.16.166407

Keywords: Aureoboletus projectellus, citizen science, Poland, fungal biogeography, ethnomycology, mushroom foraging, bolete mushrooms, fungal dispersal, invasive fungi, Polish cuisine, Does, citizen