The new genus Imsharria is proposed for a crustose species found on or near mountain summits on the Falkland Islands. It is separated from other genera of Lecideaceae by a combination of Porpidia-type asci, halonate ascospores, immersed apothecia and a hyaline hypothecium, and forms a distinct branch in the phylogenetic analysis using the markers nrITS and mtSSU. The single species, I. orangei, is characterized by its innate apothecia with a brown disc and a thallus containing norstictic acid and an amyloid (I+ violet) medulla. In addition, Porpidia imshaugii is described for a species from the Falkland Islands resembling P. skottsbergiana but with larger ascospores, and Porpidia navarina is shown to belong in the genus Poeltiaria, with the new combination Poeltiaria navarina being made. A key to the Lecideaceae on the Falkland Islands is provided.

The new species Aspicilia malvinae is described from the Falkland Islands. It is the first species of Megasporaceae to be discovered on the islands and only the seventh to be reported from South America. It is distinguished from other species of Aspicilia by the unusual secondary metabolite chemistry (hypostictic acid) and molecular sequence data. The collections of the new species support two lichenicolous fungi: Endococcus propinquus s. lat., which is new to the Falkland Islands, and a new species of Sagediopsis with small perithecia and 3-septate ascospores c. 18–20 × 4–5 μm, which is described here as S. epimalvinae. A total of 60 new DNA sequences obtained from species of Megasporaceae (mostly Aspicilia) are also introduced.

Eleven new species of crustose, lichenized fungi are described from the Falkland Islands (Islas Malvinas). Nine species are saxicolous, whereas Lecania vermispora occurs on the stems of Hebe elliptica and Tephromela lignicola is lignicolous on fence posts. The new species are: Bacidia marina, with a sordid blue-green K−, N+ violet epihymenium and acicular, multiseptate ascospores; B. pruinata, with pruinose apothecia and multiseptate ascospores; Buellia gypsyensis, with a thallus containing 5-O-methylhiascic acid and with Amandinea-type conidia; Cliostomum albidum, with pruinose apothecia lacking pigments; C. longisporum, with long narrow ascospores (c. 20 × 3 µm); Coccotrema rubromarginatum, with a placodioid thallus having a red-brown margin and lower surface; Hymenelia microcarpa, with minute, immersed apothecia (<0·1 mm diam.) and a trebouxioid photobiont; Lecania vermispora, with vermiform, 3–6 septate ascospores; Lepra argentea, with papillate isidia with dark caps; Rhizocarpon malvinae, which is similar to R. reductum but with a grey thallus, generally sessile apothecia with a thick raised margin and often with the Cinereorufa-green pigment in the epithecium and upper exciple; and Tephromela lignicola, a sterile, sorediate species on fence posts. Most of these species are reported only from the Falkland Islands although Coccotrema rubromarginatum is also reported from Isla de los Estados and Isla Grande de Tierra del Fuego, Argentina. Ascoconidia are reported from Lepra argentea and cephalodia from Pertusaria pachythallina. Keys to the species reported from the Falkland Islands in the genera of the newly described species are also provided.

Ten new species in nine different genera are described from the Falkland Islands (Islas Malvinas): Bryonora granulata with a finely granular thallus containing perlatolic acid; Bryoria mariensis, a terricolous species with norstictic acid and unusual cortex cells; Carbonea hypopurpurea with a K+ purple hypothecium and a thallus containing confluentic and 2′-O-methylperlatolic acids; Caloplaca megalariicola lichenicolous on Megalaria grossa; Cladonia flammea with a red-orange coloration on the lower side of the primary squamules; Cliostomum falklandicum, on rocks and with a dispersed thallus containing only atranorin; Lepraria malouina with usnic and stictic acids; Rimularia andreaeicola, over bryophytes and lacking lichen substances; R. subpsephota, similar to R. psephota but with a discrete white thallus lacking norstictic acid; and Usnea austrocampestris, a straggling species in sect. Neuropogon from the mountain tops. Rimularia andreaeicola is also known from Tierra del Fuego and R. subpsephota from Tierra del Fuego and South Georgia, but the other species are known only from the Falkland Islands. The new combinations Carbonea agellata, C. subdeclinans, Cliostomum aeruginascens and C. violascens are also made; Lecidea interrupta Darb. and Lecidea protracta Darb. are reduced to synonymy with Lecanora xantholeuca (Müll. Arg.) Hertel; Rhizocarpon simillimum is reported for the first time from the Southern Hemisphere, from the Falkland Islands and New Zealand; and Bryoria chalybeiformis is reported for the first time from the Falkland Islands.