Perspectives in the new Russulales

Abstract

The Russulales is one of 12 major lineages recently elucidated by molecular sequence data in the homobasidiomycetes. The order is morphologically most diverse, containing a remarkable variety of sporophore forms including resupinate, discoid, effused-reflexed, clavarioid, pileate, or gasteroid and hymenophore configurations from smooth, poroid, hydnoid, lamellate, to labyrinthoid. Functionally these fungi are primarily saprotrophs but others are ectomycorrhizal, root parasites and insect symbionts. A phylogenetic analysis of the nuclear 5.8S, ITS2 and large-subunit rDNA genes comprises the best information to date on relationships of taxa within the Russulales. Two large sister groups encompassing 11-13 major clades have been recovered within the Russulales. Based on molecular and morphological data 12 families and approximately 80 genera have been identified, although placement of many taxa has not yet been determined. The two clades containing ectomycorrhizal taxa, corresponding to the Russulaceae and the Albatrellaceae, represent the greatest diversity of sporophore morphologies. The primarily pileate lamellate family Russulaceae is nested with resupinate species and also contains pileate sequestrate, gasteroid annulate and pleurotoid forms. Albatrellaceae similarly contains resupinate poroid, pileate poroid and pileate labyrinthoid sporophores. Presence of gloeoplerous hyphae containing fluid that typically stains black in sulfoaldehyde compounds is a synapomorphy for the Russulales. Amyloid reactions in spore or hyphal walls that occur frequently throughout the Russulales often are perceived as an obvious synapomorphy but are inconsistent. Approaches including sequencing functional genes, analysis of gene expression and biochemical analysis across the entire order are needed.