Mosses are small flowerless plants that usually grow in dense green clumps or mats, in damp or shady locations. The individual plants are usually composed of simple, one-cell thick leaves, covering a thin stem that supports them but does not conduct water and nutrients (nonvascular). They do not have seeds or any vascular tissue. At certain times they produce thin stalks topped with capsules containing spores. They are typically 1–10 cm tall, though some species are much larger, like Dawsonia, the tallest moss in the world, which can grow to 50 cm in height. Moss gametophytes have stems which may be simple or branched and upright or prostrate. Their leaves are simple, usually only a single layer of cells with no internal air spaces, often with thicker midribs. They do not have proper roots, but have threadlike rhizoids that anchor them to their substrate. Traditional uses of mosses included as insulation and for the ability to absorb liquids up to 20 times their weight.