Liverworts are non-vascular plants related to mosses and hornworts. They share with their cousins a number of unique characteristics, including small size, restriction to microhabitats, and an adaptation called “desiccation tolerance”.

Desiccation tolerance is the ability to completely dry out and yet come to life minutes after they are re-wetted. Unlike other plants, liverworts don’t have thick outer cuticle that prevents water loss. This allows liverworts to survive on rock surfaces or tree bark that do not hold water very long after a rainfall.

Liverworts have a complex life cycle, starting with a spore, then producing a mass of filaments (protonema), maturing in a gametophore (“gamete-bearer”) plant that produces the sex organs. These organs are either male (antheridium) and protected by specialized cells called a perigonium, or female (archegonium) and protected by a perichaetum. Liverworts may have both female and male organs on the different individuals (dioicous) or are monoicous, where sex organs are borne on different branches of the same plants. In either case, the sperm must move where they are produced to the archegonium where the eggs are held. The sperm of liverworts is biflagellate (they have two tail-like flagellae that enable them to swim short distances provided that at least a thin film of water is present). Their journey may be assisted by the splashing of raindrops.

Liverworts are so named because they resembled lobed livers to early observers! In fact, only a portion of the liverworts known to be present in the NWT have the “lobed liver” look. These are the thallose liverworts. The other group is the leafy liverworts, often confused with mosses. Leafy liverworts are smaller and have distinct leaves arranged neatly along a stem.

Unlike most plants, liverworts are not able to produce wood (cellulose), which provides plants with the rigidity to grow to enormous size. So, liverworts are destined to remain small. They are not able to compete for light and water with plants that grow much larger and taller; however, their small size allows them to grow in places where there is less competition. These small places are called microhabitats and they often differ significantly in temperature and humidity (and nutrients) from the entire landscape.

These small plants have a role in the landscapes where they occur. Liverworts can be ubiquitous in our forests. The species Marchantia polymorpha can form large blankets of green soon after a forest fire and are thus important in erosion prevention. Other species can form significant soil crust ecosystems in extreme environments, such as in our polar regions.