Nordic Juncicolous Mycosphaerellae

Abstract

Mycosphaerellae are very important constituents of the rich mycoflora on Juncus. The most common species is M. perexigua (Karst.) Johans. Originally described from Spitzbergen, on J. biglumis, it has turned out to be widely distributed also in lowland areas and on many species of Juncus. It is generally recognized by its narrow spores with two distinct oil globules in each cell. Next in importance is M. juncellina Munk, so far only known from the type collection (Denmark, J. squarrosus). In macroscopic appearance, the latter is very much like M. perexigua but it is easily recognized by the large spores. It is found to be fairly common all over Scandinavia on several Juncus species. However, it is not well positioned in Mycosphaerella, as it possesses interascal threads. It seems to be more closely related to Monascostroma bacillifera (Karst.) O. Erikss. The name Monascostroma is untenable, as it is based on an anamorph. Other Mycosphaerellae are sometimes encountered, like M. cfr. recutita (Fr.) Johans. and the plurivorous M. tassiana (De Not.) Johans.