Recently, Mandyam and Jumponnen reviewed studies on the distribution and frequency of DSE interactions in plant communities of different ecosystems. Although it seems that DSE fungi are present in all major biome types and climate regions, studies on their presence and diversity is sporadic. One of the pioneering and landmark studies of DSE fungi focusing on alpine biomes hypothesized that the abundance and importance of plant-DSE fungi interactions increase with increasing abiotic stress on the environment. This hypothesis was integrated into the scientific canon and was strengthened by the general view that melanin content is related to abiotic stress, especially drought stress. Fungi with melanized cell walls were used in experimental studies showing increased resistance to heat and drought stress. These data and the presence of these fungi in certain habitats resulted in the general view that DSE fungi could play important roles in ecosystems with low water availability. Several studies on root-colonizing fungi of such areas �C majority of them represents North American biomes �C focused on DSE and other root associated fungi. In the mycorrhizal status studies of plant communities of the Great Hungarian Plain, the majority of the plant species was found to be colonized by DSE fungi. One of the areas studied is a semiarid open sandy grassland with forest steppe patches, and represents a characteristic ecosystem of the plain of the interfluves of the two main rivers of the Carpathian basin, the Danube and Tiscia. From a botanical point of view, this is one of the most studied habitats of the region; in addition to the lengthy vegetation studies, one of the three long-term ecological research projects in Hungary has been performed here. These grasslands are the westernmost representation of the Eurasian steppe belt. The soil is Danube-origin loose sand with very low organic matter content and almost no clay content. in ecosystems is limited and not as well understood as that of the common root colonizer mycorrhizal fungi or the previously mentioned grass endophytes. Thus, it has very limited water-holding capacity that results in a harsh environment, especially during the hot summers. The area is considered semiarid, and the open grasslands have semidesert characteristics. During the mycorrhizal status studies in this semiarid sandy grassland, 89 plant species were studied; 63 of these were found to be colonized by melanized, septate hyphae, and microsclerotia were detected in 36 species. Due to the frequent colonization, we assumed that DSE fungi play an important role in this ecosystem. These results prompted us to study the compositional diversity of DSE fungi colonizing the plants of these semiarid sandy areas.