The Arrhenia peltigerina complex—preliminary report

Phylogenetic study of Arrhenia peltigerina revealed a complex of seven divergent clades. Type specimens of Agaricus peltigerinus and Omphalina cupulatoides fell into separate clades; the latter was recombined as Arrhenia cupulatoides. Four clades were described as new species: Arr. baltica, Arr. fennoscandica, Arr. mohniensis, and Arr. talpoides; the fifth, with only a single specimen, was left formally undescribed. These cryptic species are uncommon—more so in North America than Scandinavia—and collections are often misidentified. Spore measurements separated Arr. baltica from the others by its narrower spores; average measurements help separate some species a bit better than ranges. So far, Arr. peltigerina was found only in North America, Arr. mohniensis and Arr. talpoides in both Europe and North America, and the remainder only in Europe. The host species of Peltigera was Peltigera hymenina for Arr. cupulatoides, Peltigera rufescens for Arr. baltica, and varied for the others. All but one collection came from soil over calcareous bedrock. Small sample size does not permit assigning high confidence to noted interspecific differences; these await confirmation by greater experience from future study.