Basidiospore Form in the British Species of Clitopilus, Rhodocybe and Rhodotus

Abstract

The taxonomic and nomenclatural problems of the genera Clitopilus (Fr. ex Rab.) Kummer, Rhodocybe R. Maire and Rhodotus R. Maire have proved to be involved and controversial. Kummer (1871: 23) raised Agaricus Fr. subgenus Clitopilus Fr. ex Rab. to generic level, placing it amongst the pink-spored genera. Several species which are now segregated under Rhodocybe, e.g. A. popinalis Fr. and A. mundulus Lasch were included, in addition to the type species of the subgenus, A. prunulus Scop. ex Fr. The distinctive appearance of the spores was first utilized taxonomically by Fayod (1889: 389) when describing the tribe Fusisporeae (as Fusispores) to accommodate species with fusoid spores, often bearing meridional ridges. Three genera were included, namely Hexajuga Fayod, for Clitopilus prunulus (Scop. ex Fr ) Kummer; Octojuga Fayod, for the small pleurotoid species; and Fusispora Fayod for Lepiota sistrata (Fr.) Quil. Kuhner (1926: 158) eliminated the last-named genus when erecting the tribe Jugasporeae (as Jugapords) in his goniosporous series. Hexajuga and Octojuga were retained for several years as taxonomically viable genera, with emphasis placed on the number of meridional ridges borne by the spores, and Singer (1936: 327) gave a new status to Kiihner's tribe in raising it to family level, Jugasporaceae (Kiihn.) Singer. Meanwhile Heim (I 934: 86) proposed a new family, Rhodogoniosporaceae to accommodate the other pink, goniosporous agarics. This name, however, was never validly published according to the International Code of Botanical Nomenclature Art. 32. Singer (1946: 547) restricted the Jugasporaceae to Clitopilus, leaving Rhodocybe species in the Tricholomataceae. It was suggested that the Jugasporaceae formed a very natural group and links with the Paxillaceae were proposed on the basis of size and shape of the spores, structure of the hymenophoral trama, context consistency, and the initially involute margin. At the same time, the close similarity to the Rhodogoniosporaceae, regarding spore print colour, odour, and the frequency of unpigmented species could not be overlooked. A new tribe, Orcelleae (as Orcellis) was proposed by Kuhner (1946: 193) to include those genera whose spores appear distinctly pinkish in the mass yet hyaline under the light microscope, and have basidiocarps lacking velar structures. Clitopilus, Rhodocybe and Rhodopaxillus R. Maire were included, and Rhodopaxillus was further subdivided to form two natural groupings: (a), typical forms with clamp-connexions and uninucleate spores, e.g. R. panaeolus (Fr.) Maire, R. irinus (Fr.) Metrod, and R. nudus (Bull. ex Fr.) Maire;