Bryophytes

Bryophytes (liverworts and mosses) are small, simple land plants of damp, shady places, like moss on a wet wall. They are called the amphibians of the plant kingdom: like frogs, they live on land but still need water to reproduce sexually, because their male gametes must swim to the egg.

They have no true root, stem or leaves, and no xylem or phloem. The body may be a flat thallus or have leaf-like parts; it is held to the ground by thread-like rhizoids.

The main plant you see is haploid: it is the gametophyte, the stage that makes gametes. Male organs (antheridia) make antherozoids with two flagella. The flask-shaped female organ (archegonium) holds one egg. After fertilisation, the zygote grows into a sporophyte made of a foot, seta and capsule. The sporophyte is not free-living: it stays attached to the gametophyte and gets its food from it. Inside the capsule, meiosis makes spores, which grow into new gametophytes.

• Liverworts (Marchantia): flat, thalloid, with an upper and lower side. They also multiply asexually by small green buds called gemmae, formed in gemma cups.
• Mosses (Funaria, Polytrichum, Sphagnum): a spore first grows into a green thread, the protonema; then an upright leafy stage with leaves in a spiral. Their sporophyte is more elaborate than a liverwort's.

Why they matter: some are food for animals. Sphagnum gives peat, used as fuel and as packing material because it holds water. With lichens, mosses are among the first plants to grow on bare rock, starting the making of soil. Their thick mats on the ground also reduce soil erosion.