Only recently it has become obvious that microorganisms are third, major partners in ant-plant interactions (Defossez et al. 2009; Mayer& Voglmayr 2009; Ruíz-Gonzalez et al. 2011; Voglmayr et al. 2011). It has been demonstrated that fungi (Chaetothyriales, Ascomycota) are frequently cultivated in patches located in the nesting spaces (domatia) which tropical ant-plants (myrmecophytes) provide for their resident ants. This group of fungi comprises many taxa with remarkable physiological abilities and are extremotolerant. We work on the taxonomy, and evolution of black yeast-like fungi, with emphasis on possible lines of adaptation to the ant hosts in general. In the Azteca-Cecropia association we investigated the transmission mode and specificity of the cultivated fungi.