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Fungal research on non-lichenized taxa in xeric and other unusual habitats for fungi is comparatively scarce but constantly reveal an enormous ecological and functional adaptiveness of these organisms to extremes. This holds true in the topmost forest canopies as well as in marine, arctic, antarctic or desert habitats. In the present study dried leaves of Populus euphratica from a continental desert area in Central China were investigated for endophytic fungi 6 weeks after sampling by cultivation of small leaf fragments. Thirty-five species, many of them well-known from extreme environments, were delimitated from as few as 58 isolates by a combined analysis of morphotypes, micromorphology and ITS sequences. Meta-analyses revealed pronounced conspecificity to endophytes from Populus tremula leaves, but significant differences to foliar endophytic assemblages in Pinus monticola and Fagus sylvatica. The deduced high similarity of endophytic communities on both Populus species compared with that on Pinus and Fagus suggests that many fungal phyllosphere species show a well-pronounced host preference, at least for their endophytic stages. In addition, it demonstrates that leaving leaves as a microhabitat might provide similar conditions such as constantly high relative humidity, regardless of the surrounding climatic conditions. The evolution of extremotolerance might be of particular importance for retaining competitiveness of foliar endophytes in deciduous host trees after loss of pathogenicity.