The Lichenologist 40(2): 105–109 (2008)  2008 British Lichen Society doi:10.1017/S0024282908007482 Printed in the United Kingdom Acaroconium punctiforme gen. sp. nov., a new lichenicolous coelomycete on Acarospora species and Sarcogyne regularis Jana KOCOURKOVA u and David L. HAWKSWORTH Abstract: The coelomycete Acaroconium punctiforme gen. sp. nov. is described from four members of the lichen-forming family Acarosporaceae, three species of Acarospora and Sarcogyne regularis. The new fungus is characterized by pycnidial conidiomata with a distinct ostiolar collar, enteroblastic conidiogenesis, and the production of simple brown conidia. The separation of the fungus from other somewhat similar pycnidial fungi growing on lichens and plant material is discussed. Key words: Acarosporaceae, Czech Republic, Germany, Lichenoconium, lichens, Microsphaeropsis, Slovakia, Thailand, USA Introduction Lichens continue to be a source of novel genera of associated fungi, and here we report on an unusual coelomycete dis- covered on two genera of Acarosporaceae, Acarospora and Sarcogyne, and occurring in both central Europe and North America. Methods Specimens were studied using a Nikon zoom stereo- microscope and an Olympus BH–2 research micro- scope fitted with Nomarski differential interference contrast optics and a drawing tube. Preparations and measurements were made on material mounted in water, and lactofuchsin and lactophenol Cotton blue, both after warming. Conidial measurements are given in the form ‘(minimum–) mean minus standard deviation—mean—mean plus standard deviation (–maximum)’; the number of conidia measured is indicated by ‘n’. Taxonomy Acaroconium Kocourk. & D. Hawksw., gen. nov. MycoBank no.: MB511401 Generi Lichenoconium et Microsphaeropsis s. str. simile, sed differt pycnidiis cum regionibus ostiolis atrobruneis, et conidiis latis ellipsoideis. Cellulae conid- iogenae enteroblasticae et non annellatae, conidia laeves. Typus: Acaroconium punctiforme Kocourk. & D. Hawksw. 2008 Conidiomata pycnidia, occurring singly but sometimes juxtaposed, black, sub- globose, immersed to partly erumpent, ostiolate, with a distinctly thickened ostiolar collar; superficial mycelium absent. Pycnidial wall of polyhedral angular pseudoparenchy- matous cells, individual cells reddish brown to brown. Conidiophores absent. Conidio- genous cells lining the inside of the pycnidial cavity, hyaline, broadly short-ampulliform, apex with a periclinally thickened collar, not proliferating and lacking annellations. Conidia enteroblastic, arising singly, not forming chains, broadly ellipsoid, non- septate, colourless at first but becoming pale brown inside the pycnidial cavity, smooth- walled, rounded at both ends and lacking any basal scar or frill. J. Kocourková: Mycological Department, National Museum, Václavské náme ˇstí 68, Praha 1, CZ-115 79, Czech Republic. Email: jana_kocourkova@nm.cz D. L. Hawksworth: Departamento de Biología Vegetal II, Facultad de Farmacia, Universidad Complutense de Madrid, Plaza Ramón y Cajal, Ciudad Universitaria, 28040 Madrid, Spain; and Department of Botany, Natural History Museum, Cromwell Road, London SW7 5BD, UK.