Fungal endophytes are a highly diverse and ubiquitous group of organisms which colonize the tissues of all plants. Their interaction with plants range from pathogenic to mutualistic depending on the genetic background of both partners, their developmental stage and diverse environmental factors, but hitherto our knowledge on their ecological function is very scarce. In this work we focused on root endophytes because their colonization is systemic and prone to be involved in the host's uptake of nutrients, and hence they are likely to affect plant development. We studied the interaction patterns of 128 root endophytes from diverse taxa and origins, with the brassicaceous plants Arabidopsis thaliana and Microthlaspi perfoliatum and the poaceae Hordeum vulgare, in order to identify associations with relevant ecological functions. For each combination, we measured the effect of fungal colonization on plant's weight and symptoms development, and assessed quantitatively and qualitatively the fungal growth within roots. Additionally we measured endophytes' cellulolytic activity and growth rate as potential factors influencing the outcome of their interaction. All endophytes tested were able to colonize the plant roots of the three hosts under the assayed conditions, but most of them did not affect significantly plant development. When effects were found, these were mostly detrimental and could be attributed to specific fungal taxa, which displayed a differential behavior across the plants tested. We are currently contrasting these results with the endophytes' phylogeny and with data about their ecological origin in order to extract conclusions on their potential roles in natural ecosystems.