title: Resolved phylogeny and biogeography of the root pathogen Armillaria and its gasteroid relative, Guyanagaster.
abstract: Armillaria is a globally distributed mushroom-forming genus composed primarily of plant pathogens. Species in this genus are prolific producers of rhizomorphs, or vegetative structures, which, when found, are often associated with infection. Because of their importance as plant pathogens, understanding the evolutionary origins of this genus and how it gained a worldwide distribution is of interest. The first gasteroid fungus with close affinities to Armillaria-Guyanagaster necrorhizus-was described from the Neotropical rainforests of Guyana. In this study, we conducted phylogenetic analyses to fully resolve the relationship of G. necrorhizus with Armillaria. Data sets containing Guyanagaster from two collecting localities, along with a global sampling of 21 Armillaria species-including newly collected specimens from Guyana and Africa-at six loci (28S, EF1α, RPB2, TUB, actin-1 and gpd) were used. Three loci-28S, EF1α and RPB2-were analyzed in a partitioned nucleotide data set to infer divergence dates and ancestral range estimations for well-supported, monophyletic lineages.
  
  
  
  The six-locus phylogenetic analysis resolves Guyanagaster as the earliest diverging lineage in the armillarioid clade. The next lineage to diverge is that composed of species in Armillaria subgenus Desarmillaria. This subgenus is elevated to genus level to accommodate the exannulate mushroom-forming armillarioid species. The final lineage to diverge is that composed of annulate mushroom-forming armillarioid species, in what is now Armillaria sensu stricto. The molecular clock analysis and ancestral range estimation suggest the most recent common ancestor to the armillarioid lineage arose 51 million years ago in Eurasia. A new species, Guyanagaster lucianii sp. nov. from Guyana, is described.
  
  
  
  The armillarioid lineage evolved in Eurasia during the height of tropical rainforest expansion about 51 million years ago, a time marked by a warm and wet global climate. Species of Guyanagaster and Desarmillaria represent extant taxa of these early diverging lineages. Desarmillaria represents an armillarioid lineage that was likely much more widespread in the past. Guyanagaster likely evolved from a gilled mushroom ancestor and could represent a highly specialized endemic in the Guiana Shield. Armillaria species represent those that evolved after the shift in climate from warm and tropical to cool and arid during the late Eocene. No species in either Desarmillaria or Guyanagaster are known to produce melanized rhizomorphs in nature, whereas almost all Armillaria species are known to produce them. The production of rhizomorphs is an adaptation to harsh environments, and could be a driver of diversification in Armillaria by conferring a competitive advantage to the species that produce them.
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Koch
authors.affiliation: Sam Mitchel Herbarium of Fungi, Denver Botanic Gardens, Denver, CO, 80206, USA.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Wilson
authors.affiliation: Institute of Agricultural Research for Development (IRAD), National Herbarium of Cameroon (MINRESI), PO Box 1601, Yaoundé, Cameroon.
authors.forename: Olivier
authors.initials: O
authors.lastname: Séné
authors.affiliation: Department of Biological Sciences, Humboldt State University, Arcata, CA, 95521, USA.
authors.forename: Terry W
authors.initials: TW
authors.lastname: Henkel
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA. maime@purdue.edu.
authors.forename: M Catherine
authors.initials: MC
authors.lastname: Aime
mesh_terms: D000349:Africa; D055392:Armillaria / Q000145:classification*; D001487:Basidiomycota / Q000145:classification*; D002980:Climate; D019143:Evolution, Molecular; D006172:Guyana; D010802:Phylogeny; D058974:Phylogeography; D018517:Plant Roots / Q000382:microbiology*; D017422:Sequence Analysis, DNA
keywords: Armillaria root rot; Cameroon; Eocene; Fungal taxonomy; Gasteromycetation; Guiana Shield; Melanin; Mushroom evolution; Physalacriaceae; Systematics