Liverworts are small plants related to mosses. Nearly 300 species are native to the British Isles, but broadly liverworts can be divided into two types: thallose and leafy. Thallose liverworts have a flattened, plate-like body – the thallus – and no leaves. A common example is Marchantia, which is often topped with weird, umbrella-like sexual organs.
Leafy liverworts have two ranks of flattened leaves growing out from a stem. A third rank of smaller, forked leaves lies on their underside.
Liverworts
Liverworts, such as Marchantia and Pellia, can be a problem in gardens; in beds they can compete with plants, on the lawn they can cause areas of grass to die and they can make patios and other hard surfaces treacherously slippery.
They can quickly establish and multiply under conditions of high humidity, high soil moisture, low pH and little plant competition, especially where the soil is compacted. They are found mainly infesting pot plants but can often be found in borders where the soil has gradually become impoverished.
Cultural control
With pots and containers it is a simple task periodically to remove the liverwort and top up with fresh compost or add a top dressing of coarse gravel.
In the garden the soil pH should be kept close to neutral (pH 7) which is suitable for most plants other than rhododendrons and similar lime-haters. Borders and other cultivated areas should be well stocked with plants and regularly hoed and raked in order to maintain a rough and well-drained surface. Where soil compacts readily after rain the organic content of the soil can be improved by digging in or mulching with coarser materials such as well-rotted farmyard manure, garden compost or composted bark.
Chemical control
In lawns
If liverwort is present on lawns it is likely that the lawn is badly compacted and unless this problem is addressed the liverwort will simply re-grow.
In borders
Products based on fatty acids (Bayer Advanced Mosskiller) or pelargonic acid (Finalsan Moss & Algae Killer or Weedol Max) should be used with care around garden plants as any chemical applied to the foliage of ornamental plants will cause scorching.
On hard surfaces
Liverworts can be controlled by repeated spraying with proprietary formulations of pelargonic acid (Finalsan Moss & Algae Killer), acetic acid (Doff Fast Acting Natural Weed Spray), or nitrilo triacetic acid/trisodium salt (Bayer Path & Patio Cleaner), which are approved for the control of mosses, algae and similar growth.