Mosses are small flowerless plants that typically grow in dense green clumps or mats, often in damp or shady locations. The individual plants are usually composed of simple, one-cell thick leaves, attached to a stem that may be branched or unbranched and has only a limited role in conducting water and nutrients. Although some species have vascular tissue this is generally poorly developed and structurally different from similar tissue found in other plants. They do not have seeds and after fertilisation develop sporophytes (unbranched stalks topped with single capsules containing spores). They are typically 0.2–10 cm (0.1–3.9 in) tall, though some species are much larger, like Dawsonia, the tallest moss in the world, which can grow to 50 cm (20 in) in height.