Fungi are highly diverse both phylogenetically and in terms of the functions or roles they perform in natural environments. While fungi are most commonly known for their capabilities as decomposers, members of this kingdom are also involved in other aspects of nutrient cycling and can serve as important ecological mediators through interactions with other organisms [1]. The fungal kingdom is large and diverse, with estimations of fungal species ranging from 2.2–3.8 million [2] to 11.7–13.2 million [3], depending on the methods used and the definition of species considered. Since 1990, genetic classification of fungal species has been common, and the concept of phylogenetic monophyly (i.e., all organisms with a common ancestor and possessing the same mutations belong to the same species) has been widely applied when designating species [4]. The use of multiple phylogenetic markers within genomes [4] and Genealogical Concordance Phylogenetic Species Recognition (GCPSR) [5] has shown to result in the most precise taxonomic classification and strategy for discriminating species. As our ability to identify and distinguish fungal species increases in accuracy and efficiency, so does our understanding of how fungal biodiversity contributes to important ecological functions in natural environments.
True morels (Morchella spp.) are socially and economically important worldwide and are widely consumed as edible and medicinal fungi [6]. Morel taxonomy has been revised multiple times based on morphological, ecological, and biogeographical characteristics, and most recently based on phylogenetic analyses involving multiple loci [7]–[9]. Phylogenetic investigations have demonstrated that multiple morel species can share macromorphological traits and closely related species may display distinct ecological or morphological features relative to one another [9]. Fruiting body morphology in morels, which has also been considered in species identification, is influenced by environmental factors (i.e., humidity, light, temperature, and soil) and also varies depending on the developmental stage [10]. In addition, different modes of sexual reproduction have been discovered even within a single species of morel. This is the case for Morchella importuna which includes secondary homothallic (self-fertile) and heterothallic (self-sterile) specimens [11]. Finally, intraspecific ecological variation can also exist; for instance, Morchella sextelata and Morchella importuna, are both fire-adapted but can be cultivated independent of fire events [11]. New morel species continue to be described from all continents using integrative phylogenetic approaches [12]–[14]. While many described species appear to be invalid based on phylogenetic and phenotypic criteria (e.g., Morchella crassipes, Morchella costata, Morchella elata, Morchella conica), the genus Morchella still includes about 80 different recognized species [9].
One of the other features that has been highlighted in many taxonomic studies of Morchella is the endemic nature of populations from distinct geographical locations [7], [15], [16]. Therefore, describing the phylogenetic diversity of Morchella in specific geographic regions might be particularly valuable in fields such as conservation biology. While fungi are often not considered in conservation programs, fungal populations also experience pressures caused by habitat destruction, climate change, and pollution [17]. Although climate change might appear to have a positive effect on morel’s distribution range in China [18], it may have the opposite impact in other locations. The Global Fungal Red List Initiative includes Morchella anatolica as critically endangered, because of its very limited distribution range, rarity, overexploitation, and habitat loss due to the destruction of its natural habitat (i.e., eastern Mediterranean basin) (http://iucn.ekoo.se/, accessed the 13.12.2022). Studies of M. anatolica have been critical for understanding the evolution of morels, as members of this species represent basal lineages of Morchella [19].
Invasive microbial species, although not necessarily pathogenic, are those that colonize new geographic areas and impact local ecosystems, through over-competition for resources or ecological niches, or hybridization [20]. The high level of regional endemism of Morchella spp. [7], [21] is a critical feature when considering the impact of potential invasive species. Less than ten morel species have a cosmopolitan distribution range [21], and this cosmopolitan range is likely due, at least for some of them, to the impact of human activities [22]. For instance, Morchella galilaea and M. importuna were likely introduced in non-native areas through human cultivation, as they are often reported from greenhouses, gardens, and landscaped areas [21]. Morchella americana and Morchella populiphila were possibly introduced in Europe from North America in association to Populus spp. plantations [8]. Similarly, Morchella eximia and Morchella tridentina could have been introduced from the USA to South America along with North American trees [23]. Morel species from the Esculenta clade form mycorrhizal-like [24] or endophytic interactions with plants, and can therefore be introduced inadvertently with the trade of plants [21].
Switzerland is one of the European countries in which the biodiversity of morel populations has never been assessed using genetic approaches. In the scientific literature, very few morels from Switzerland have been reported or analyzed. A specimen of Morchella norvegiensis (named Morchella eohespera strain M510) was reported from Davos (canton of Grisons, Switzerland) [25]. This specimen was held in the German Collection of Cell Cultures (DSMK), but the sampling date was not recorded [25]. From the same canton, specimens apparently belonging to the yet unresolved Morchella inamoena ss Clowez were collected under Populus tremula [26]. Based on a morphological identification, Röllin and Anthoine (2001) reported M. tridentina as a rare species found in Bex (canton of Vaud). A specimen of Morchella esculenta (strain PhC198) was collected in Malval along the Allondon River (canton of Geneva, Switzerland) in early May 2004 [8]. M. americana and Morchella rufobrunnea were also reported from studies conducted in Switzerland [9]. In a book describing the macroscopic ascomycetes from Switzerland [28], four species were described: Morchella deliciosa (named Morchella conica var. deliciosa), M. esculenta, Morchella semilibera (named Mitrophora semilibera), and a rare species named M. elata (the latter being considered as a synonym of M. importuna [8]), which could effectively correspond to M. importuna given its ecology, fruiting month, and morphology. In another book from the same year, several morels collected in Switzerland were described [29]: Morchella purpurascens was collected at 2000 m on the canton of Valais; the postfire morel M. eximia was collected the canton of Jura near a fireplace; Morchella dunalii (named Morchella rielana) was apparently widespread in the alpine region of Switzerland; Morchella atrotomentosa, a possible synonym for Morchella tomentosa (according to morphological and ecological descriptions) or M. importuna (according to Clowez and Moreau (2018)), was collected in abundance after an exceptional forest fire in the canton of Valais; M. esculenta (named Morchella pseudoumbrina) was collected in Valais under Corylus; M. esculenta (named Morchella hetieri) was collected in a mixed forest in the canton of Vaud.
In this study, the biodiversity of Swiss morel populations was established by a combination of field sampling, morphological and genetic characterization of the specimens collected. Establishing a database describing the biodiversity of morels in Switzerland is crucial to be able to monitor species and their populations, to identify strains adapted for local cultivation, and to assess the risk of potential invasions of non-native species, which are at the time of writing the only ones being used for morel cultivation in Switzerland. We hypothesized that morel species already reported from the surrounding countries (e.g., France, Italy, Germany), such as M. esculenta, Morchella vulgaris, Morchella deliciosa, or M. eximia would be found in Switzerland. Due to the high continentalism of Morchella species, previously undescribed lineages were also expected to be discovered. Both hypotheses were met, as four described species (M. esculenta, M. deliciosa, M. pulchella, M. importuna) and five new phylogenetic lineages (Morchella sp. Mel-43 to Mel-47) were found.