A new sooty blotch was found in Israel on various Citrus species and varieties. The fungus causing the sooty blotch was described as Caenothyrium citri n. sp. of the Microthyriaceae family. The fungus produces dimidiate perithecia which are attached to the substrate by a narrow marginal membrane not developing any air mycelium. The walls of the perithecia are hyaline and radiate, the upper half of which is covered by darker hyphae and by two to three alternate rows of setae. The asci are bottle-necked, and contain 4-8 four-celled spores. The spores are hyaline, elliptical, μ10-18 × 5-7. The generic and specific taxonomy of Caenothyrium citri was discussed and verified. Attention was drawn to the fact that the Microthyriaceae family which has a tropical distribution, developed two species in the Mediterranean region: the above described Caenothyrium in Israel and an other species of Microthyrium in Italy. This being a phytogeographical phenomenon noticed many times in other fungous groups of tropical distribution.