Green-tongue liverwort (Marchantia polymorpha) is a common, weedy species that is native to BC. You will frequently see it growing in wet areas often on exposed mineral soil. Common habitats include wet forests, streamside habitats as well as heavily disturbed areas with wet mineral soil including cutblocks and ditches. It is also frequently seen growing on the soil surface of nutrient-rich mineral soil of potted plants in nurseries.

Unlike leafy liverworts that have stems and leaves, green-tongue liverwort is an example of a thallus liverwort that lacks a distinct stem and consists of flaps of tissue.

Looking closely at the thallus surface, you can see a fine pattern of diamond-shaped areas with a single pore in the center. These pores allow gas exchange with an open chamber under the thallus surface that are packed with a loose arrangement of chlorophyllous cells which helps to reduce evaporation. These pores do not have guard cells and cannot open and close like the stomata of vascular plants.

Another interesting feature of green-tongue liverwort are the cup-shaped structures produced on the thallus surface that contain several disk-shaped gemmae. These are specialized bodies and are a form of asexual reproduction where each gemma can grow into a new plant. They are dispersed by rain drops striking the gemmae cup similar to the structures seen in bird’s nest fungi.

A lot of people wonder why I would bother to study such insignificant plants but sometimes these plants can be an important feature of the landscape. Several years ago I was on Mount Kobau near Osoyoos where a wildfire had destroyed a stand of Douglas-fir on the lower south-facing slope. Normally, these stands are very dry in the summer and consist of open stands of Douglas-fir with bluebunch wheatgrass in the understorey. The summer following the fire, the weather had been cool and moist. I visited this area in September and saw a dead stand of Douglas-fir with nothing in the understorey but a carpet of green-tongue liverwort which had invaded and dominated the forest floor. This was shocking as this species requires cool, moist conditions to grow and would never normally be associated with these dry Douglas-fir stands.

Ninety-nine percent of the forest floor in the above photo consists of green-tongue liverwort – an amazing population explosion. The summer following my visit was very dry and all of these plants would not have survived the dry conditions and would have disappeared from the site.