Diversity of fungi on Taiwanese fern plants: review and new discoveries

In this review, chances and challenges of investigating fungi on ferns in Taiwan are presented and discussed. Taiwan with a high species number of more than 800 fern species (including lycophytes here) as well as high density of fern plants is an ideal environment for studying the scarcely known fungi that depend as saprotrophs, symbionts and parasites on ferns. In Taiwan only ca. 60 fungi have been recorded on ferns. If we apply the overall estimated average plant-fungus species ratio of ca. five fungi per plant species in a given area, about 90% of fern-associated fungi have not yet been identified in Taiwan. Ca. 30% of fern-associated fungi recorded in Taiwan are rust fungi (Pucciniales, Basidiomycota) and further ca. 10% ascomycetes (Mycosphaerellales), all comprising highly specialized plant parasites. About 3.5% are species of discomycetes (Helotiales, Ascomycota) with most of them being more or less specific saprobic decomposers of dead fern tissues. The illegitimate name Pseudocercospora christellae Haldar & J.B. Ray for a parasitic fungus from India is replaced by the new name Ps. cyclosori. The new name Asterocalycella is proposed for the illegitimate genus Asterocalyx (Helotiales, Ascomycota). A new white mutant of A. mirabilis saprobic on Cyatheaceae is recorded. DNA sequence analysis suggests excluding this genus from the Sclerotiniaceae. Specimens of further Helotiales (Lachnum oncospermatum, Lachnum sp. and Microscypha sp.) from the same decaying leaf are presented as examples for the specific diversity and its incomplete taxonomic knowledge. The new species Teratosperma dicranopteridis found on living Dicranopteris linearis illustrates the difficulty to assign higher taxonomic ranks and specific ecological roles to some fungi.