Liverworts and hornworts are significant in New Zealand, but often overlooked or mistaken for mosses. In New Zealand these small plants grow from the coasts to alpine zones, but most abundantly in rainforests. In the past, they were grouped with mosses under the name bryophytes. We now known that, although they share common features, liverworts, hornworts and mosses evolved independently.
Four key features are common to liverworts, hornworts and mosses, and distinguish them from more complex plants such as ferns, conifers and flowering plants:
- They lack specialised fluid-conducting tissues (xylem and phloem). That limits their size, because they cannot draw water and mineral nutrients more than about half a metre up their stem.
- Their water-producing cells are not stiffened with lignin.
- The plant in their life cycle that produces spores is smaller and attached to the plant that produces sex cells.
- The spore-producing plant is unbranched and bears a single spore capsule.
In common with all plants, liverworts and hornworts have a life cycle with two generations. The green plant that we call a liverwort or a hornwort produces sex cells (eggs and sperm). Inside the green plant an egg and sperm unite into a single cell, which then begins to grow into a spore-producing plant. This new plant remains attached to its parent, which it depends on it for water and nutrients.