Meylania 16 17 Floristik zenb.) P. James, Bacidia rubella (Hoffm.) A. Massal., B. subincompta (Nyl.) Ar- nold, Bactrospora dryina (Ach.) A. Massal., Dimerella pineti (Schrad. ex Ach.) Vězda, Verrucaria viridigrana Breuss. in Ukraine. In Switzerland, A. borystheni- ca was found in a deciduous mixed stand managed as coppice-with-standards forest (Canton of Zug) and in a beech forest (Canton of Ticino). Characteristic epiphytic species include Agonimia allobata, Lecanora subrugosa Nyl., Opegra- pha atra Pers., Opegrapha vermicellifera (Kunze) J.R. Laundon, Pertusaria leio- Agonimia borysthenica, a new lichen species (Verrucariales) to Switzerland Lyudmyla Dymytrova, Christine Keller & Christoph Scheidegger Meylania 49 (2012): 16-18 Résumé Agonimia borysthenica n’est connu que du basin du fleuve Dniepr en Ukraine, où il a été trouvé sur de l’écorce de chêne. Agonimia borysthenica a maintenant été découvert dans le canton de Zoug et est mentionné ici pour la première fois en Suisse. Abstract Agonimia borysthenica was so far known from the Dnipro River basin in Ukraine where it was found on bark of Quercus robur. Agonimia borysthenica has recently been found in the canton of Zug and is reported here for the first time to Swit- zerland. Zusammenfassung Agonimia borysthenica war bisher vom Flussgebiet des Dniepr in der Ukraine be- kannt, wo die Art auf der Borke von Quercus robur gefunden wurde. Agonimia borysthenica wurde kürzlich im Kanton Zug neu für die Schweiz nachgewiesen. During a field trip to an old-growth oak forest (Huenenberg, Canton of Zug) where the vulnerable species Bactrospora dryina (Ach.) A. Massal. is growing, we found the recently described species Agonimia borysthenica. To date, it was known only from the type locality in Ukraine. This additional locality broadens our knowledge about the ecology and distribution of this species. A revised description, which includes information about habitat requirements and the distribution of this spe- cies as well as some illustrations are presented below. Agonimia borysthenica Dymytrova, Breuss & S.Y. Kondr. Description: Thallus rather thick, granular, greenish grey to dark grey. Thalli- ne goniocysts 0.6-0.8 (-0.9) mm diam., convex, swollen to bullate, distinctly discrete or partly confluent in a granular crust. Cortical cells of goniocysts 5-10 μm, often with small papillae. Photobiont chlorococcoid. Perithecia very small, 0.17-0.22 (-0.25) mm in diam., black, matt, smooth throughout, ovoid or pyriform, with a short smooth neck and a pale top, sessile to 1/3 immersed. Asci 8-spored, 130-140 × 40-60 μm, with minutely granular matrix. Ascospores muriform, colourless, ellipsoid, 40-55(75) × 15-24 μm. Ecology: The species grows on mosses and mossy bark of old deciduous trees, espe- cially Quercus and Fraxinus, in shaded and humid habitats in old-growth forest stands. Agonimia borysthenica was found together with Agonimia allobata (Sti- Fig. 1. Agonimia borysthenica Dymytrova, Breuss & S.Y. Kondr. A: thallus with perithecia (part of holotype specimens, KW, scale bar: 1 mm); B: thalline goniocyst, C: muriform ascospores. A B C