Agaricus chionodermus Pilát, a species new to Bulgaria

The article presents the first record of Agaricus chionoderma Pilát in Bulgaria. Basidiomata of the species were found on June 2004, September 2010, and September 2011 in the Thracian Lowland floristic region. The article brings closer taxonomic profile, ecological requirements and distribution pattern of the species. Differences from similar species are discussed. It also describes macroscopic and microscopic characteristics of the discovered specimens and presents the specification of habitat the fungus concerned. The species are described and illustrated by photographs of macroscopic and microscopic features on the basis of Bulgarian specimens.

In the course of studies of the diversity of genus Agaricus in Bulgaria, A. chionodermus was found by the author for the first time.It is presumably a rare species for many countries of Europe and yet not well known.Therefore in this paper a detailed description and illustrations are presented including features that distinguish A. chionodermus from similar species.This work adds a new species to the Bulgarian agarics, namely A. chionodermus Pilát, one of the about seventy "European" species which, according to Cappelli [4], belong to Agaricus sect.Arvenses.

Material and methods
Air-dried studied specimens of the fungus are kept in the mycological collection of the Agricultural University-Plovdiv (SOA).Basidiomata of species were photographed with SONY Cyber-shot.
Description of morphological characters of basidiomata is based on fresh and dried specimens.Micromorphological features were observed and measured in fresh and dry fragments of tissues dehydrated in water, under an Amplival ML light microscope, with magnification ×1000.Microphotographs were taken on Amplival ML.Drawings were made with the aid of a drawing tube under an oil-immersion objective.Spores were examined in Melzer's reagent and were taken from the spore print for measurements.Calculated values are based on 50 measurements.The obtained data for length and width of microstructures were examined by standard statistic methods [19,20] and are presented in the text in the following way: (min-) mean ±1σ (-max), n = 50, (l/w min-max ); of the basidia and cheilocystidia: min-max.
The abbreviations of the author names of fungal species are given according to Kirk and Ansell [22].Nomenclature of species follows Kirk et al. [8].The taxonomic and nomenclature decisions in the article have been made in conformity with the most appropriate taxonomic monographs of the Agaricus genera [4,23,24].
The chorological map of the occurrence of the A. chionodermus in the country, have been depicted using the program software dSOA [25].

Results and disscusion
Agaricus chionodermus Pilát has never been previously found in Bulgaria [12,26].The occurrence of first A. chionodermus basidiomata was discovered on 7th June 2004 in Thracian Lowland, Plovdiv distr., above Stryama village (Fig. 1).The area where the fungus occurred is situated along the watercourse of Stryama River and is surrounded by farmland, as well as meadows and pastures.The dominant species of the tree layer at the plant community where basidiomata of A. chionodermus has been found were: Acer campestre, Fraxinus angustifolia, Populus canescens and Tilia cordata.The shrub layer includes mainly: Populus tremula, Salix caprea, Corylus avellana and Sambucus nigra.The herb layer was dominated by cereal grasses, e.g.Carex caryophyllea, Poa pratensis, etc.
In the course of the field trial only three specimens of A. chionodermus were found.The basidiomata of the agarics were revealed in grassy vegetation, close to P. canescens (Ait.)Sm.The next finding of basidiomata A. chionodermus was done in the same place in September 2010 and September 2011.The location of the species has been carefully marked and will be monitored in the future.MACROSCOPIC AND MICROSCOPIC FEATURES.Pileus up to 7.5-12(-15) cm in diameter, thick-fleshed, initially hemispherical, subsequently convex to plano-convex, seldom flat or slightly depressed, silky finely fibrillose, sometimes cracked dry in the center, snow-white, white, sometimes greyish white in the center, slightly yellowish towards the margin.Margin undulate, initially involute, thin, with whitish silky fibrillose scales, 5-7 mm thick, finally with remnants of the partial veil.Pileipellis consisting of whitish thick-walled cylindrical hyphae, with clamps, 5-10 μm in diameter.Gills free, thin, crowded, narrowing toward the margin of pileus, long, with an even edge, whitish-pink, subsequently light pink, gray-pink to dark-brown, with light, sterile edge.Hymenophoral trama in young basidiomata initially regular, latter irregular, consisting of cylindrical, thin-walled hyphae, 5-12 μm in diam.Stipe up to 8-15 × 1.5-3 cm, central, cylindrical, with or without slightly bulbous base, initially white, subsequently ± white, smooth to silky-fibrillose, yellowish at touch.Flesh whitish, on cutting becoming lemon-yellow in the base of the stipe.Ring wide apical, fleecy, free standing, whitish, with touch upper layer yellowish tinge and thick, delicate, sericeous, bottom layer.Context in pileus and stipe fragile, whitish.Smell non-distinctive, very faint, non of almonds.Taste non-distinctive.TAXONOMICAL REMARKS.Nearly identical basidiomata produces A. arvensis Schäeffer known to be common in Europe, which can be separated with certainty from A. chionodermus by the cap being generally snow-white, wide sericeous ring and the slightly larger spores [1,4,23], but mainly on the base of microscopic characters.As emphasized by Cappelli [4], A. chionodermus in contrast to, A. arvensis has round and conspicuous cheilocystidia.Moreover, there is an ecological difference between the two species, i.e. A. chionodermus grows on periphery of deciduous and coniferous forest, or forest meadows, on calcareous and sandy soils, while A. arvensis occurs on humus rich soil, mainly among grasses.Agaricus nivescens (F.H. Møller) F.H. Møller also resembles A. chionodermus, from which it mainly differs by habitat (terrestrial fungus occurs mainly in grasslands on calcareous soil), almonds and fungoid smell, indeterminate taste, and smaller size of spores and basidiomata [4,27].
Metric and macroscopic data of Bulgarian specimens of A. chionodermus agree with the descriptions of [4] and [23].
According to this investigation, A. chionodermus should be considered as a species developing in grassy vegetation on forest meadows at lower elevation, close to poplar, possibly also under other broadleaved tree species.The observations are in accordance with the literature data that A. chionodermus should be considered as species developing mostly on basic to neutral or sandy soil [4].
HABITAT, ECOLOGY, PHENOLOGY, EDIBILITY STATUS.Basidiomata of A. chionodermus almost exclusively appears in summer to early fall season (May-October), solitary, in periphery of deciduous forest or forest meadows and grassy vegetation, 200-700 m alt.Humus saprotroph, mostly on basic to neutral or sandy soil.There are some information that this species is edible without gastrointestinal problems [4,28].There is so far no indication in Bulgaria that its edibility is known and presently the fungus is unlikely to be collected for food, beside if not be confused with other similar species.

Conclusion
Agaricus chionodermus should be especially sought after in plains and lowlands regions of the country, but its presence in other parts of Bulgaria cannot be excluded.Basidiomata of this fungus might have been misidentified because of its resemblance to other similar Agaricus species from section Arvenses, especially if a spore print was not available.
This new finding contributes to the diversity of Bulgarian mycobiota, by adding new Agaricus records and might be useful for creating a database of the Bulgarian sabulicolous Agaricus species.

Fig. 2
Fig. 2 Basidiomata of Agaricus chionodermus at different stages of development in situ from Bulgaria (photos: M. Lacheva).