Next, in the 1930s, only two species of Laboulbeniales were reported in the Netherlands: Laboulbenia cristata Thaxt. from Paederus riparius (Linnaeus, 1758) (Kossen 1936, 1938) and Laboulbenia flagellata Peyr. from Platynus spp. (Zaneveld 1938). It was not until Abraham Middelhoek (1906–1968) that the number of reported species of Laboulbeniales in the Netherlands would increase by 25 (Middelhoek 1941, 1942, 1943a, b, c, d, 1945, 1947a, b, 1949). Middelhoek was first an artist who, among other things, made stained glass windows. Only after World War II, he studied biology and raised an interest in fungi, particularly the Laboulbeniales. After Middelhoek, Laboulbeniales were forgotten about in the Netherlands except for a single paper by Meijer (1975), who proposed to use Laboulbeniales fungi as “biological tags” to trace migration patterns. Since 2012, Haelewaters and colleagues have published several papers dealing with Laboulbeniales in the Netherlands, which together have more than doubled the number of reported species in this country (De Kesel and Gerstmans 2012; Haelewaters 2012, 2013; Haelewaters et al. 2012a, b, 2014, 2015a, b, 2020; De Kesel et al. 2013; Haelewaters and De Kesel 2013; De Kesel and Haelewaters 2014, 2019; Haelewaters and van Wielink 2016). To date, 79 species of Laboulbeniales are reported from the Netherlands.
In this contribution we compile all available data from Belgium and the Netherlands. Keeping in mind that both countries show some geographical differences, especially due to specific soils and increasing altitude in the southern part of Belgium, we think a combined checklist makes sense at this point. This is mainly because the sampling effort for Laboulbeniomycetes in the southern part of Belgium has been much lower compared to the northern and central areas of the country (De Kesel et al. 2020). As a result, the bulk of Belgian and Dutch records come from biogeographically comparable regions. The here presented checklist is useful to illustrate where mutual gaps need to be filled and what the impact has been of the chosen strategies (fieldwork, museum collections) and trapping techniques. In combination with the recently published Belgian catalogue (De Kesel et al. 2020) presenting illustrations and identification keys to 115 taxa, this checklist will serve as a reference for mycologists, students, and scholars studying Laboulbeniomycetes fungi. In addition, this work is an appropriate starting point for an updated checklist of thallus-forming Laboulbeniomycetes from Europe–an ongoing project that needs to be updated, three decades after the massive undertaking of Santamaría et al. (1991).
Materials and methods
Specimen collection and morphological study
Insects were collected in Belgium and the Netherlands using pitfall traps and on an illuminated white screen at night. Specimens were preserved in 96–99% ethanol until they were screened for presence of thalli of Laboulbeniomycetes at 20–50× magnification. Thalli were removed from the host at the foot and mounted in Amann solution
