The algae of a threatened peat bog in Modlniczka near Kraków, situated in the Wyżyna Krakowsko-Częstochowska upland in Poland, are described, illustrated and briefly discussed. The 216 taxa reported from the peat bog include 159 species and varieties, and 35 morphotypes of chrysophyte stomatocysts; 22 algae are identified only to genus level.
One species, Trachelomonas elliptica (Playfair) M. Deflandre, is new to Europe. Nine species are new to Poland: in Chrysophyceae, Ochromonas sphagnalis W. Conrad, O. tenera H. Mey.; in Bacillariophyceae, Diploneis petersenii Hust. and Navicula pseudobryophila (Hust.) Hust.; in Euglenophyta, Phacus balatonicus Hortob., Lepocinclis cf. spirogyra Korshikov and Trachelomonas cf. komarovii Skvortzov; and in Chlorophyta, Closterium dianae Ehrenb. ex Ralfs cf. var. brevius (Petkoff) Willi Krieg. and C. parvulum Nägeli var. cornutum (Playfair) Willi Krieg.
New to the Wyżyna Krakowsko-Częstochowska upland are 33 species: in Cyanophyta, Oscillatoria maior Vaucher and O. utermoehliana (Utermöhl) Elenkin; in Chrysophyceae, Ochromonas mutabilis G. A. Klebs, Chrysococcus tessellatus F. E. Fritsch and Dinobryon divergens O. E. Imhof; in Xanthophyceae, Botrydiopsis arhiza Borzí, Botryochloris minima Pascher, Gloeobotrys chlorinus Pascher and G. limneticus (G. M. Sm.) Pascher; in Bacillariophyceae, Adlafia bryophila (J. B. Petersen) Lange-Bert., Brachysira brebissonii R. Ross, Cavinula variostriata (Krasske) D. G. Mann & A. J. Stickle, Chamaepinnularia soehrensis Krasske var. hassiaca (Krasske) Lange-Bert., Eucocconeis flexella (Kütz.) Cleve var. alpestris (Brun) Hust., Eunotia implicata Nörpel, Lange-Bert. & Alles, E. meisteri Hust., Fragilaria famelica (Kütz.) Lange-Bert., Frustulia crassinervia (Bréb.) Lange-Bert. & Krammer, Navicula festiva Krasske, Neidium hercynicum Art. Meyer, Pinnularia divergentissima (Grunow) Cleve, P. stomatophora (Grunow) Cleve, P. viridiformis Krammer and Sellaphora pseudopupula (Krasske) Lange-Bert.; in Cryptophyta, Cryptomonas obovata Skuja; and in Chlorophyta, Elakatothrix genevensis (Reverdin) Hindák, Schroederia planctonica (Skuja) Philipose, Closterium praelongum Bréb. var. brevius (Nordst.) Willi Krieg., Cosmarium pachydermum J. W. G.Lund var. minus Nordst., C. vexatum W. West, Euastrum ansatum Ralfs var. pyxidatum Delponte, Pleurotaenium nodulosum (Bréb.) de Bary and Pleurotaenium trabecula (Ehrenb.) ex Nägeli var. crassum Wittr.