Species of Apiognomonia are some of the most ubiquitous leaf-associated fungi of broad-leaved trees of the northern temperate zone. Especially widespread and diverse is Apiognomonia errabunda, found mostly on beech, oak, and linden. This species and its closest relatives are known for their complicated phylogenetic relationships that have caused considerable confusion in the past. In the present paper, we describe the results of a three-gene-based reconstruction of phylogenetic relationships between A. errabunda, A. veneta, and A. hystrix for 373 isolates. Using combined information from the nuc rDNA internal transcribed spacer region ITS1‐5.8S‐ITS2 (ITS barcode) and intron regions of actin (ACT) and calmodulin (CAL) genes for 263 isolates, we confirmed the occurrence of host-associated lineages within A. errabunda. However, the clustering of isolates by host species was incomplete: some isolates occurred on the “wrong” hosts and a number of isolates carried mixed genetic profile, indicating substantial level of inter-host group recombination. In addition, a number of isolates were identified as putative, pending further verification, interspecies hybrids between the much more divergent A. errabunda and A. hystrix. Key Words: Anthracnose, endophyte, leaf-associated fungi, phylogeny
