Agaricus xanthodermus Genev., syn.: Agaricus pseudocretaceus Bon, Psalliota grisea (A. Pearson) Essette, Agaricus pearsonianus Contu & CurreliYellow Stainer, DE: Karbol-Egerling, KarbolchampignonSlo.: karbolni kukmakDat.: Sept. 25. 2018Lat.: 46.358153 Long.: 13.700662Code: Bot_1159/2018_DSC3378Habitat: abandoned pasture, partly overgrown with bushes and trees; slightly inclined mountain slope, south aspect; sunny, dry and relatively warm place; calcareous, colluvial, skeletal ground; exposed to direct rain; average precipitations ~ 3.000 mm/year, average temperature 7-9 deg C, elevation 565 m (1.850 feet), alpine phytogeographical region.Substratum: soil.Place: Lower Trenta valley, between villages Soa and Trenta, right bank of river Soa, near abounded farm house Strgulc, Soa 47, East Julian Alps, Posoje, Slovenia EC. Comments: I find difficult to determine species names of genus Agaricus. If you search for taxon names pertaining to this genus in Index Fungorum for example you will get in return 6.000 different names! In the field the mushrooms shown here had unmistakably unpleasant smell and taste on chemicals (usually called phenolic or carbolic); measured spores fit well to Agaricus xanthodermus; the pilei had typical trapezoid form in vertical section (particularly when young), which also fits to this species. Yet, there are also problems: the habitat is not typical, it should be woods, but I found this fruit bodies in grassland; though the staining after cutting or damaging the fruit bodies was yellowish, it was only very faint, even in the base of the stipe, where it should be immediate and strong chrome-yellow. Stipe base of this observation shows a conspicuous rim and is quite flat at the bottom (marginate-bulbous), which is, according to several sources, typical for Agaricus essettei (now joined to Agaricus silvicola according to IF). Such stipe base may occasionally occur also with Agaricus xanthodermus according to Ref.: 1, and 2. Interestingly, two months after this observation, in dry state, smell changed completely to pleasant, on spices, similar on celery. However, not on anise or bitter-almonds, which is characteristic for some other species of this genus.Alternatively, this find could eventually be Agaricus campestris since it was found in grassland, but its spores are larger (6.5-8/4-5.5 or 6.4-7.9/4.4-5.6 according to Ref.: 2). Similar Agaricus essettei Bon (now Agaricus sylvicola) with typical stipe base as found in this observation, also has somewhat larger spores and doesn't show trapezoid pilei (at least not according to Ref.: 1). So, Agaricus xanthodermus seems promising, but not certain.Several pilei found; hut diameter (not expanded) 5-9 cm; stipe 5.5-11 cm long and 14-20 mm in diameter, bulb 28-32 mm diameter, fibrous, very faintly bruising yellowish; taste strong, unpleasant, long lasting, on chemistry (phenol); smell unpleasant, on chemistry when fresh, when dry (after 2 months) pleasant, on spices, celery? SP abundant, dark brown, oac637. Old gills become dark violet-brown. Spores smooth. Dimensions: (5,1) 5,5 - 6,7 (7,4) (3,1) 3,4 - 4,1 (4,4) m; Q = (1,4) 1,5 - 1,8 (1,9); N = 40; Me = 6 3,7 m; Qe = 1,6. Olympus CH20, NEA 100x/1.25, magnification 1.000 x, oil; in water, fresh material. AmScope MA500 digital camera.Herbarium: Index Herbariorum LJF @ Mycotheca and lichen herbarium of Slovenian Forestry Institute.Ref.: (1) G.J. Krieglsteiner (Hrsg.), Die Grosspilze Baden-Wrttembergs, Band 5., Ulmer (2010), p 166. (2) J. Breitenbach, F. Kraenzlin, Eds., Fungi of Switzerland, Vol. 4. Verlag Mykologia (2000), p 529. (3) M. Bon, Parey's Buch der Pilze, Kosmos (2005), p 278. (4) R. Phillips, Mushrooms, Macmillan (2006), p 243.