Tropical lowland cloud forest (TLCF) occurs in moist river valleys in French Guiana, below 400 m, and has never been described. The forest resembles mixed lowland rain forest but differs by the frequent occurrence of fog and the abundance of epiphytes. Species richness of epiphytic liverworts in TLCF of French Guiana is similar to that at 2000 m in the Andes and is three times higher than in Amazonian lowland forest. The high species richness is explained by the favorable air moisture regime in TLCF, which allows these poikilohydric species to thrive in the hot lowland forest. Fog during day times prevents desiccation and allows the plants to reach net photosynthesis in spite of high temperatures. About thirty percent of the liverwort species in TLCF are restricted to the forest canopy and several are obligate epiphylls. Habitat preferences are similar to those in tropical montane cloud forest but taxonomic composition and total abundance are different. Dispersal by asexual reproduction is significantly more common in the forest understory than in the canopy, where dispersibility is less constrained. Canopy species have significantly wider ranges than understory species, presumably due to long range dispersal by spores.