Liverwort (Marchantia polymorpha and related species) has a long history of use in traditional medicine, particularly in East Asian and European herbal practices. Traditionally, liverwort was sometimes used to treat respiratory ailments, including coughs, bronchitis, and general symptoms related to colds and influenza. This use is largely based on the doctrine of signatures and empirical experience rather than scientific study.

There is little to no robust scientific evidence supporting the efficacy of liverwort specifically for influenza. While liverworts contain various bioactive compounds, such as terpenoids and flavonoids, only limited in vitro studies have explored their potential antiviral activity, and even these studies have not directly addressed common influenza viruses. Most references to liverwort’s use for influenza are found in ethnobotanical surveys, historical texts, and folklore rather than in rigorously controlled clinical research.

In summary, the use of liverwort for influenza is justified primarily by tradition, not by scientific validation. The evidence supporting its effectiveness for this condition is weak, with a rating of 1, reflecting anecdotal or historical use without modern clinical confirmation.