Exploring Potential Hosts of Putative Epiphytic Waxcaps

The colourful fruiting bodies of waxcaps are readily recognised components of a threatened assemblage of fungi with strict habitat requirements referred to as CHEGD-fungi thriving in the declining habitat of semi-natural grasslands. Despite waxcaps being incorporated into action plans and despite their widespread use as bioindicators, their nutritional mode for long remained a mystery. However, recent research indicates that waxcaps are systemic endophytes deriving carbon through interactions with plants. As these findings are new, details on the interactions and knowledge on the host ranges are very fragmentary. Hyphae of some waxcap species have recently been identified within tissues of Plantago lanceolata and the results of a previous field experiment on waxcaps suggest that graminoids may be important hosts for certain species of waxcaps. In this study, I explore potential hosts of three waxcap species through species distribution modelling on regional-scale and on site-scale. Based on reported field observations of seemingly obligate co-occurrences of certain plants and some CHEGD-related fungi including a waxcap, I hypothesize that waxcaps have small host ranges. The analysis revealed many potential exclusive hosts, including several graminoids. Graminoids are known to be hosts of high quality to several root hemiparasitic plants. This has been attributed to their fibrous root systems and great abundance in grasslands, facilitating root connections. I find it plausible that these host characteristics also may be beneficial for waxcaps. Other remarkable entries were Potentilla erecta, the genus Pilosella p.p., Pilosella officinarum and some ericaceous taxa potentially serving as exclusive hosts for Hygrocybe punicea. Additionally, many plant taxa occur in almost every unit of observation and could potentially serve as exclusive non-limiting hosts. None of the species found to host waxcap hyphae in previous studies appeared likely exclusive hosts of the waxcaps studied here. However, there are indications that the results may have been obscured by an inability to sufficiently consider abiotic variables and results should be interpreted cautiously. Due to suspected uncertainties in the analysis, I cannot unambiguously prove nor reject the hypothesis that some waxcaps have small host ranges. The suggested range of potential hosts could further be reduced by assessing plot-scale co-occurrences. For ultimate confirmation of biotic interactions between fungus and potential hosts I suggest continued molecular and histological analysis of plant tissues. In conclusion, this study may provide basis for further research unravelling the mystery of waxcap ecology.