Moss and fern species are common in the forest understorey but not usually found in open, dry habitats (e.g., roadside at the start of the trail). The reason for this is that both moss and fern species are relatively primitive plants that are only imperfectly adapted to a terrestrial environment. The ancestors of plants lived in the ocean and many of the characteristics displayed by modern plants represent adaptations to a terrestrial environment. Moss species, for example, have no roots to extract water from the soil nor do they have any vascular tissue to transport water within the plant. Ferns have both roots and vascular tissue and therefore, can grow larger than moss species, but like the mosses, ferns require water for reproduction. The sperm cells have flagella and must swim through a water film to fertilize the egg. This means both fern and mosses are largely restricted to fairly moist habitats like the forest understorey.
