Surprising morphological, ecological and ITS sequence diversity in the Arrhenia acerosa complex (Basidiomycota: Agaricales: Hygrophoraceae)

A molecular genetic study of the Arrhenia acerosa complex using the ITS fungal barcoding marker revealed unexpected diversity along a cascading group supporting over 20 lineages. Among these, we identified five previously described species: A. acerosa s.str., A. glauca, A. latispora, A. subglobisemen, and Rhodocybe tillii (recombined as A. tillii). We described four new species: A. fenicola from Canadian prairie grasslands, A. juncorum and A. leucotricha, both on live and dead herbaceous material in European wetlands, and A. svalbardensis from the high Arctic. All nine taxa treated here were fixed with sequenced types. In addition, we identified seven other lineages, some only represented by a single collection, requiring further study before description, and four groups of two species or more, also requiring further dissection before circumscription of their constituents. The diversity of the complex with respect to size, colour, habitat, range, distribution, and substrate preference is made more intriguing by the presence of several lineages of brown omphalinoid species, differing from the typically pleurotoid forms in this complex. We generated 97 of the 131 ITS sequences studied, adding 65 new sequences from the acerosa complex.