The present study took place in Les Baillets, an area within The Allondon river valley in the outskirts of the city of Geneva, Switzerland. It aimed to review the lichenological and bryological flora from an ecological and floristic perspective, by means of ecological targeted relevés and targeted single-specimen collections. The floristic part of this work focused on the description of rare or threatened species in Les Baillets and on presenting the different communities of the study site in relation to their environment. The ecological study investigated the effect of environmental variables on species richness and diversity, as well as seeked to reveal how these factors contribute to the definition of different communities. To this end, analyses of variance and ordination (direct gradient canonical correspondence analyses and indirect gradient non-metric multidimensional scaling) were performed. Additionally, an independent inventory of species from the genus Usnea was undertaken, and patterns of distribution were examined. Ultimately, global results were considered in the light of conservation issues, and protection measures as well as potential action plans were proposed.