Mycelial morphology, rhizomorph anatomy and primordium formation of Gymnopilus penetrans (Cortinariaceae, Basidiomycetes)

Gymnopilus penetrans (morphologically distinct from G. sapineus ) grows well on the usual culture media in Petri dishes and forms arthroconidia in slimy droplets. Dense mycelial mounds reminiscent of the dense mycelial plugs observed in the natural substrate (decaying wood of Fagus sylvatica ) develop in some cultures but fail to produce noduli and primordia. Hyphal strands do occur, but no rhizomorphs have been observed in artificial culture. The anatomy of the natural rhizomorphs extracted from the decayed wood is described. Rhizomorphs contain foreward and backward growing hyphae, vessel hyphae with incompletely dissolved septa, and some percurrent hyphae. Protein crystals are frequent. The noduli produced by the mycelial plugs in cavities in the decaying wood elongate to produce basidiome primordia. A loose outer layer envelops both, the nodulus and the young primordium. During development, this layer is slightly reinforced by hyphae growing out of the pileus and down towards the stipe, and by hyphae growing out of the stipe and up towards the pileus. The veil is therefore composed of the original loose layer (the noduloblema), the pileoblema and the cauloblema, the latter two forming the cortina of the mature basidiome. Gymnopilus penetrans therefore is amphicleistoblemate. As the hymenial cavity is formed by apoptosis of some hyphae within the primordium, G. penetrans is endocarpic. In more traditional, but less precise terms, G. penetrans is monovelangiocarpic.