Multilocus phylogenies reveal three new truffle-like taxa and the traces of interspecific hybridization in Octaviania (Boletaceae, Boletales)

Takamichi Orihara,Adriana Corrales,Matthew E Smith,Rosanne Healy

doi:10.1186/s43008-021-00066-y

Abstract

ABSTRACTAmong many convergently evolved sequestrate fungal genera in Boletaceae (Boletales, Basidiomycota), the genus Octaviania is the most diverse. We recently collected many specimens of Octaviania subg. Octaviania, including several undescribed taxa, from Japan and the Americas. Here we describe two new species in subgenus Octaviania, O. tenuipes and O. tomentosa, from temperate to subtropical evergreen Fagaceae forests in Japan based on morphological observation and robust multilocus phylogenetic analyses (nrDNA ITS and partial large subunit [LSU], translation elongation factor 1-α gene [TEF1] and the largest subunit of RNA polymerase II gene [RPB1]). Based on specimens from the Americas as well as studies of the holotype, we also taxonomically re-evaluate O. asterosperma var. potteri. Our analysis suggests that O. asterosperma var. potteri is a distinct taxon within the subgenus Octaviania so we recognize this as O. potteri stat. nov. We unexpectedly collected O. potteri specimens from geographically widespread sites in the USA, Japan and Colombia. This is the first verified report of Octaviania from the South American continent. Our molecular analyses also revealed that the RPB1 sequence of one O. tenuipes specimen was identical to that of a closely related species, O. japonimontana, and that one O. potteri specimen from Minnesota had an RPB1 sequence of an unknown species of O. subg. Octaviania. Additionally, one O. japonimontana specimen had an unusually divergent TEF1 sequence. Gene-tree comparison and phylogenetic network analysis of the multilocus dataset suggest that these heterogenous sequences are most likely the result of previous inter- and intra-specific hybridization. We hypothesize that frequent hybridization events in Octaviania may have promoted the high genetic and species diversity found within the genus.

Highlights

The Boletaceae (Boletales, Basidiomycota) is a large family that mostly consists of epigeous, mushroom-forming fungi
We critically examined the morphology and habitat of the taxon and we compared it with the previously published literature on North American Octaviania species
The overall macro-morphology, peridial structure and the basidiospore and basidia dimensions matched the original description of Octaviania asterosperma var. potteri Singer and Smith (Singer and Smith 1960), which was reported from Michigan, USA

Summary

Introduction

The Boletaceae (Boletales, Basidiomycota) is a large family that mostly consists of epigeous, mushroom-forming fungi. The genus Octaviania is comprised of sequestrate, truffle-like species that have a marbled gleba and dextrinoid or non-amyloid basidiospores with coarse, conical to pyramidal ornamentation (Orihara et al 2012a). Pegler and Young (1979) provided evidence that Octaviania is distinct from those morphologically similar sequestrate genera and Orihara et al (2012a) redefined the current generic concept of the genus. Paz et al (2016) reviewed the European species of Octaviania and critically examined the type species, O. asterosperma. Fulvoglobus introduced by Orihara et al (2012a) should be synonymized with subg. Octaviania sensu Orihara et al (2012a) should be synonymized with subg.

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