Riopa metamorphosa (Fuckel) Miettinen & Spirin

Miettinen, Otto, Spirin, Viacheslav, Vlasak, Josef, Rivoire, Bernard, Stenroos, Soili & Hibbett, David S., 2016, Polypores and genus concepts in Phanerochaetaceae (Polyporales, Basidiomycota), MycoKeys 17, pp. 1-46 : 21-24

Riopa metamorphosa (Fuckel) Miettinen & Spirin comb. nov. Figures 1dand 9

Polyporus metamorphosus Fuckel, Jb. Nassau Ver. Naturk. 27-28: 87 (1874) [ ’1873–74’].

Lectotype.

Germany. Oestrich (Nassau): Mittelheimer Vorderwald, rotten trunk of Quercus , "Herbier Fuckel 1894, Herbier Barbey-Boissier", no. 2008 (S F43290, designated here).

Epitype.

Czech Republic. Moravia: Lanžhot, Ranšpurk virgin forest, rotten trunk of Quercus robur , 5 Oct 1988 Pouzar (PRM871894, designated here, duplicate H 7008579).

Description.

Basidiocarp resupinate, white, cream or straw-colored, consistency fragile when dry. Forms patches of a few cm that can fuse to extensive basidiocarps, up to 2(-3) mm thick. Pores rounded angular, soon splitting and then irregular and sinuous, mouths smooth, 2-3(4) per mm, up to 2 mm wide when split. Subiculum very thin, arachnoid to pellicular, white to cream, often lighter than pores. Margin thinning out, usually no sterile margin.

Hyphal system monomitic, simple septate, hyphae rather homogenous throughout. Subicular hyphae interwoven, tissue loose, hyphae thin-walled to slightly thick-walled, (2.8)3.2-4.4(6.4) µm, walls rarely up to 1 µm in diameter. Tramal hyphae thin- to slightly thick-walled, interwoven but mostly vertically arranged, (2.2)2.9-3.5(4.0) µm in diameter. Subhymenium relatively loose, structure uncharacteristically simple for a polypore, composed of branching corymb-like, straight hyphae similar to those in trama. Crystals present as irregular aggregates of rhomboidal plates of various sizes, also fine encrustation present in subiculum. Shiny, hyaline, amorphous droplets floating around in CB.

Cystidia thin-walled, cylindrical, projecting above hymenial layer 5-20 µm, often covered with spores, (15)20 –50×4– 6.2 µm, born in subhymenium, poorly differentiated, appear as elongated basidioles, rare.

Hymenium loosely arranged, cells thin-walled. Basidia clavate, often projecting slightly above the rest of the hymenium, 15 –28(35)×4– 5.5(6.2) µm, with 4 sterigmata.

Basidiospores curved cylindrical, thin-walled, (4.2)5 –6.6(8.2)×(2)2.2– 3.1(3.5) µm, L=5.69 µm, W=2.59 µm, Q=2.19.

Anamorph known as Sporotrichum aurantiacum Link present or absent. Most but not all basidiocarps produce at least conidia in subiculum. When the anamorphic stage is well developed, it appears as an orange mass of conidia similar in shape to Haplotrichum aureum , in conjunction with basidiocarps or separately. Microscopically composed of thick-walled, ellipsoid to constricted conidia (8.2 –12.2×5.2– 7.8 µm, n=36/3) born singly as apical parts of slightly to clearly thick-walled, partly encrusted hyphae, (3.2)3.6-4.5(7.2) µm in diameter, walls ≤1.5 µm. The conidia and hyphae are yellow, the plasma of the conidia stains in CB, and the walls are CB− to CB(+) and slightly dextrinoid. In KOH the conidia stain pinkish red in masses. Wakefield (1952) proved in the lab that the polypore and conidial stages belong to the same organism.

Distribution.

Temperate Europe: Germany, Poland, Slovakia, Czech Republic, Russia (Nizhny Novgorod), France (mainland, Corsica) ( Vampola and Pouzar 1996, Pieri and Rivoire 1997). Northernmost records from Southern Norway ( Ryvarden and Melo 2014) and Stockholm, Sweden ( Romell 1926).

Ecology.

Grows preferably on rotten oak trunks. We have seen it on Eucalyptus and Salix caprea , also reported on Castanea , Juglands and Malus ( Bourdot and Galzin 1928, Ryvarden and Gilbertson 1993, Pieri and Rivoire 1997).

Remarks.

Fuckel’s herbarium is in Wiesbaden ( WIES), but its material is not available for loan. A duplicate of an original Fuckel specimen in Stockholm is chosen as the lectotype here. It represents an almost completely destroyed anamorphic stage. For practical reasons we also select an epitype from the Czech Republic.

Conidia have been reported from few other members of the Phanerochaetaceae: Phanerochaete chrysosporium ( Burdsall and Eslyn 1974) and Hyphodermella rosae ( Rahimlou et al. 2015). Riopa metamorphosa conidia are similar to the conidia of these species, particularly Hyphodermella rosae .