The lichen genus Chrysothrix Mont, is shown to comprise four species: C. candelaris (L.) Laundon comb, nov., C. chlorina (Ach.) Laundon comb, nov., C. chrysophthalma (P. James) P. James & Laundon comb, nov., and C. pavonii (Fr.) Laundon comb. nov. (C. noli-tangere (Mont.) Mont.). The genera Pulveraria Ach. and Temnospora Massal. are placed in the synonymy of Chrysothrix nom. cons., and all bright yellow, leprose, sterile lichens with pulvinic acid derivatives, formerly included in Lepraria and Crocynia, are referred to the genus. Chrysothrix oceanica Rasanen is excluded; it probably belongs to Caloplaca. A key to and detailed accounts of the recognized species are included. There are three chemotypes of Chrysothrix candelaris, one of which is probably of hybrid origin.

Lemmopsis is retained as a genus in the Lichinaceae. Three species are recognised, L. arnoldiana (Hepp) Zahlbr., L. oblongans (Nyl. ex Crombie) A. L. Sm. and L. pelodes (Körber ex B. Stein) comb. nov. Lemmopsis leptogiella (Nyl.) A. L. Sm. is transferred to Porocyphus. The status of Psorotichia flotowiana (Hepp) Müll.Arg. is discussed and its affinities suggested.

The new generic name Lichenothelia nom. nov. is introduced for the Microthelia aterrima group which proves to be unrelated to the corticolous mainly nonlichenized fungi generally referred to Microthelia. Two species are accepted, Lichenothelia metzleri (Lahm) comb. nov. and L. scopularia (Nyl.) comb. nov. [syn. M. aterrima (Krempelh. ex Anzi) Zahlbr.], distinguished by the ascospore size and septation, iodine reaction of the hymenial gelatin and ascus walls, and further the shape of the asci and extent of the development of the interascal filaments. The systematic position of the genus is unclear as the ascus structure shows affinities with both the Lecanorales and Dothideales. It is also uncertain whether it really should be regarded as lichenized.

Gyalectidium corticola sp. nov. is described from Costa Rica. It is the first corticolous lichen to be formally described in this primarily foliicolous genus. The structure of the ascocarps and their pattern of development is similar to the type species of the genus but it also shows some resemblance to other genera in the Asterothyriaceae in different features. Of particular note is the production of conidia within the massive muriform ascospores.

Fifteen species of the Caliciales are reported from Africa and Macaronesia. Calicium subquercinum, Chaenotheca chrysocephala, Ch. trichialis, Coniocybe furfuracea, C. gracillima, Sphinctrinella calicioides and Tylophoron protrudem are new to Africa; Calicium trabinellum and Strongyleuma exsertum are new to Macaronesia.

The species belong to two groups with respect to their distribution: (1) the borealtemperate species with a wide distribution in the Northern Hemisphere, such as Chaenotheca chrysocephala and Ch. trichialis, occur only at high elevations, usually about or above 3000 m; (2) one including, for example, Tylophoron moderatum, T. protrudens and Schistophoron—species occurring at low or moderately high elevations with a subtropical/tropical distribution.

A study of the weathering phenomena brought about by the growth of Lecanora alra on a substrate of magnesium silicate minerals (serpentinite) has been carried out mainly by X-ray diffraction and scanning electron microscopy. The lichen thallus contains appreciable amounts of crystalline magnesium oxalate dihydrate, which occurs as an insoluble extra-cellular precipitate and derives from the decomposition of magnesium silicates (particularly chrysotile) by oxalic acid secreted by the mycobiont. In theory magnesium oxalate dihydrate should be capable of incorporating large amounts of heavy metal ions into its structure, as indeed the electron probe evidence indicates has happened, thus suggesting a mechanism for enabling some lichens to cope with environments that are high in these generally harmful ions. The only weathering product detected in the lichen weathering crust is an X-ray amorphous silica gel which often retains the fibrous morphology of the chrysotile from which it forms.

The past and present occurrence of Usnea longissima has been investigated at 31 localities in an area of eastern central Sweden. A marked decline was found which is due to different forestry practices, and, to a minor extent, air pollution. The species is confined to old spruce forests, mainly located on north-facing slopes with a slightly oceanic climate. The population size showed a large variation both within and between seven investigated localities. Specific habitat demands and low dispersal ability make U. longissima very sensitive to environmental disturbances.