Gymnopilus ianthinilophus (Agaricales, Basidiomycota), a new species from the Brazilian Amazon

Abstract Gymnopilus is an agaricoid genus of mostly wood-rotting mushrooms, with ca. 200 species worldwide distributed, of which 23 of them are currently known in Brazil. In the Amazon region, Gymnopilus taxa correspond mostly to very old names described under Agaricus, later recombined into Gymnopilus, such as G. marasmioides, G. panurensis, G. psamminus, and G. trailii. Based on the examination of a well-annotated exsiccate at the INPA Herbarium, Gymnopilus ianthinilophus is described as a new species. It is characterized by the densely cespitose habit, squarrose pileus with blackish brown squamules, adnate to subdeccurent lamellae with decurrent tooth, violaceous brown stipe, weakly dextrinoid basidiospores 7.6-9.2 × 5.1-6.1 µm, interwoven pileus trama, lageniform with capitate or subcapitate apex cheilocystidia measuring 15.3-25.5 × 5.6-8.2 µm, and absence of pleurocystidia and caulocystidia. Description, photographs, illustrations of the new species, and discussion and comparison with morphologically similar taxa are provided.

Following our investigations of Gymnopilus in Brazil (e.g., Silva-Junior & Wartchow 2015;Fabrini & Wartchow 2020;Fabrini et al. 2022), we begun to analyze exsiccates of Gymnopilus included in the unpublished thesis made by Aguiar (1984) and deposited in the INPA Herbarium (Thiers, continuously updated).One of them corresponds to an interesting material provisionally named as "Gymnopilus violaceus I.J.Araújo ined."(Aguiar 1984) growing caespitose on a decayed trunk in the Amazon forest, and is formally described here as Gymnopilus ianthinilophus.
Thus, this report emphasizes in the importance of inventories in biological collections, as such herbaria, that are important source of knowledge of the biological diversity (Peixoto & Morim 2003).
The species is densely cespitose on a dicotyledon trunk.And is know only from the type locality.The etymology is from Gr. 'ianthinus' (= violet) and 'lophus' (= tuft).Due the new species is disposed as a dense tuft of many basidiomata with violet stipe.
This species was originally described as "G.violaceus Araújo ined." in the unpublished thesis of Aguiar (1984), due the violet stipe.In addition, the epithet chosen by us also emphasizes the cespitose habit of the basidiomata.In the original description, Aguiar (1984) reported dextrinoid basidiospores, but in our analysis, the weak Melzer's reaction was observed after approximately 24 hours.
Species with dark colored stipe are not common in Gymnopilus.Gymnopilus picreus (Pers.)P. Karst., G. picreus sensu Hesler, G. marasmioides, and G. russipes Pegler are the only few known species, so far: The North American specimens of G. picreus sensu Hesler somewhat agree in the ornamented pileus centre, and also share in the subdecurrent lamellae and the pigmented stipe.However, G. picreus sensu Hesler differs in the 'subsquamulose' pileus with moist and hygrophanous surface, umber to fulvous stipe, radial pileus trama, and the presence of ventricose pleurocystidia and clavate pileocystidia (Hesler 1969).
In the Brazilian Amazon, G. marasmioides might be a somewhat similar species.It was originally described with tawny pulverulent subconic pileus, emarginate to adnate lamellae, and deep brown stipe (Berkeley 1856, as Agaricus marasmioides Berk.).Later, it was redescribed in detail by Singer (1965), who reported as growing in fasciculate tuft, but with tawny subglabrous and minutely sulcate pileus in dried state with a distinct papila, adnate to emarginate lamellae, and exannulate rusty stipe with deep brown base when dry. Microscopically, the basidiospores are similar to G. ianthinolophus in size measuring 6-9 × 4.8-6.5 µm, but the species presents pleurocystidia.Subsequent type study by Pegler (1988) also reported basidiospores 7-9 × 4-5.6 (7.5 ± 0.4 × 5.2 ± 0.3) µm, and numerous subcylindric to lageniform pleurocystidia.Thus, the presence of pleurocystidia in G. marasmioides can be readily used for segregating this taxon from G. ianthinilophus.
Finally, G. russipes was reported as very common growing in large numbers on rotten Rodriguésia 74: e01612021.2023 wood in the islands of Martinique and Guadeloupe (Pegler 1983).This species was described with a reddish brown stipe, a feature that can be somewhat similar to the violaceus brown stipe of G. ianthinilophus, as well as the absence of veil and of pleurocystidia.However, G. russipes differs at least in the larger, up to 60 mm in diam., pileus, with minute apressed fibrillose surface, and wider basidiospores 8-10 × 6-7.5 µm, L = 9 µm; W = 6.5 µm; Qm = 1.34 (Pegler 1983).