Deciphering interfungal relationships in the 410-million-yr-old Rhynie chert: Brijax amictus gen. et sp. nov. (Chytridiomycota) colonizing the walls of glomeromycotan acaulospores

Abstract

Glomeromycotan spores from the Early Devonian Rhynie chert frequently contain evidence of colonization by other fungi. However, relatively few of these relationships have been described and evaluated. Brijax amictus gen. et sp. nov., a probable chytrid (Chytridiomycota) associated with certain thick-walled archaeosporalean acaulospores from the Rhynie chert, develops largely within the host spore wall. Thalli are eucarpic, monocentric, 16.5–40(−50) μm high, and consist of an inoperculate sporangium (zoosporangium or resting spore stage) located in the outer, ephemeral spore wall component, and a rhizoidal system that extends into the persistent spore wall. Sporangia that, at maturity, are completely surrounded by the host spore wall develop a prominent discharge tube, whereas ones not covered by the host wall have simple openings or pores. Thallus morphology resembles certain present-day species of Rhizophydium (Rhizophydiales) and Phlyctochytrium (Chytridiales); however, the systematic affinities of B. amictus remain unresolved. This discovery contributes to the understanding of the various levels of interfungal relationship that existed in early terrestrial ecosystems.