Moss is a small, soft plant that forms silky, green tufts of moderate size on rocks, roots of trees, decaying logs, tree trunks, or the soil of forest floors in damp, shady locations. There are approximately 12,000 known moss species throughout the world. Moss such as this is autotrophic and undergoes the process of photosynthesis. Moss absorbs water and nutrients through its leaves, unlike other plants that absorb nutrients from their roots. Their lack of vascular systems means that moss requires high moisture levels to survive. Also, in order to grow and reproduce, they transfer spores. Without plenty of moisture, they cannot complete fertilization and the transfer of spores will cease.