Cryptogamie, Mycol., 1999,20 (4): 283 289 O 1999 Adac/Editions scientifiques et mddicales Elsevier SAS. Tous droits #serv€s "Pleospora" aquatica, a new lichenicolous fungus on Aspicilia supertegens from Siberia Mauro TRETIACH & Pier Luigi NIMIS DiparTimento di Biologia, Ilniversitd degli Studi di Trieste, Va Giorgieri, 10, 34127 Trieste, haly Fax: + 39 040 568 855; tretiach@univ.trieste.it (Received 15 March 1999, accepted 30 May 1999) Abstract - The lichenicolous furrgus "Pleospora" aquatica is described as new. It grows parasitically on thalli of Aspicilia supertegens, and is known only from tle type locality, in the iunkinski ridge (central Sibeda). Is is tentatively referred to the genus PkoJpora on account of its phaeodictyospores and of the anatomy of pseudotheria. o 1999 Adac/Editions scientifiques et m6dicales Elsevier SAS Dacompia I licienicolcllts f]umgi I Pleospora I Pleosporaceae I sysbmalircs R6sum6 - Une nouvelle espice de champignon lichdnicole non lichdnis€, Pleosporu aquatica' esl ddcrite. Elle parasit€ le thal]r d'Aspiciti.t superreSen s et n'est connue que dans la localit6 type, dans la chaine de Tunkinski (Sib6rie centrale). Elle est plac€e, avec h6sitation, dans le genre Pleospora sur la base de ses phaeodictyospores et de la structure de ses pseudotheces. @ 1999 Adac/Editions scientifiques et medicales Elsevier SAS Dacampia I chanpignon lich6nicole / Pleospora I Pleosporuceae I syst6matiques 243 INTRODUCTION During the summer of 1997, the authors took part in a field rip in the Bajkal region, organizid by Dr Tatjana Makryi (Novosibirsk) in cooperation with the Depart- m;nt of Biology of the Trieste University. Some areas near the springs of the river Tubota, on the Tunkiniky ridge, were visited. In a single locality the authors collected a peculiar licbenicolous fungus, occurring on thalli of an aquatic Aspicilia, which proved to be a new species. It is tent;tively referred to the genus Pleospora on account of its anatomy, and oi its spore-characters. The formal description is given herein. MATERIALS AND METHODS Measurements given in mrn were taken on dry material at the dissecting microscope, while those given in pm are microscope measurements of hand-cut sections, or of squash preparations. Ascospores, hamathecial filaments, etc. wele measured at