Alien Fungi of Europe

This chapter deals with fungi in the broad sense, i.e. organisms studied by mycologists, including species classified within three different eukaryotic kingdoms: Eumycota, Chromista (or Stramenipila) and Protozoa (Whittaker 1969; Cavalier-Smith 1986; Worral 1999). Lichen forming fungi are considered in Essl and Lambdon (2009). Fungi are a major component of biodiversity on Earth, as the second largest group of Eukaryotes, after insects. The number of fungal species has been estimated to be at least 1.5 million, but less than 10% have been described (Hawksworth 2001). Fungi are inconspicuous organisms and have been far less studied than mammals or vascular plants. This also applies to invasion ecology: fungi are usually poorly, if at all, represented in alien species databases, with the exception of a few well-known examples of plant or animal pathogens. In particular, few comprehensive national checklists have been published for Europe (see below). The reasons for this low representation are most likely due to a poor knowledge of this group of organisms rather than a low invasion success (Desprez-Loustau et al. 2007). When undescribed species are found, how likely is it that they are native to the geographic location of their first record? The species concept itself is not easily handled in fungi. Fungal taxonomy has been evolving rapidly over the recent years, in particular with the use of molecular tools and phylogenetic analysis. This can be illustrated by the fact that more than 50% of the fungal species in the dataset compiled in DAISIE were described (or subjected to taxonomic revision) after 1950, and almost 20% only in the 2000s. Many fungal species previously defined on the grounds of morphology (or of symptoms on host plant for pathogens) have been shown to be a complex of several cryptic species differing in their ecology, and especially in their geographic range (Pringle et al. 2005). A recent example is Mycosphaerella pini, a foliar pathogen of pines, which was shown to be a complex of two phylogenetic species, with one found worldwide, while the other is restricted to the North-Central USA (Barnes et al. 2004). The poor knowledge in the biogeography of fungi can make it difficult to determine what is an alien species. Within the DAISIE dataset, more than 30% of fungal species are considered as cryptogenic, i.e., of unknown origin. New approaches, including phylogeography, might provide clues on the native range of species. For example, Phytophthora ramorum, recently discovered both in Europe and North America, is assumed to be alien in both regions, on the basis of a multilocus analysis demonstrating an extremely narrow genetic structure, most likely explained by the introduction of a few closely related genotypes (Ivors et al. 2006)