Agaricus geesterani, spec. nov. A very remarkable agaric discovered in the Netherlands

For several years now a very striking agaric is known to occur in the Netherlands that baffles every mycologist who has the luck to see it. As one of us (P.H.) never had this luck, the present study is based on thorough examinations of the material by the other author, while for the rather precarious taxonomic decisions both authors are to be held responsible. At first sight the present species resembles a large Agaricus bitorquis, but on closer examination the differences are obvious and manifold. There is however no doubt about the fact that it belongs to the Agaricaceae. It combines microscopical characters of the (sub)tropical genus Micropsalliota with a type of basidiocarp like that of the heaviest species of Agaricus. We think, however, that it should not be classified in Micropsalliota but in Agaricus, where because of its aberrant characters a new section has to be created for it.