From the plant kingdom, vascular plants are the most thoroughly explored taxon from a phytochemical and pharmacological point of view, but bryophytes, taxonomically placed between the algae and the pteridophytes and belonging to the non-vascular plants, are less well studied. The fact that bryophytes are not damaged by insects, microorganisms, slugs, snails and mammals suggests that these plants contain bioactive secondary metabolites that have toxic or repellent effect against other species. However, the pharmacological profiles of the majority of species are undisclosed, intensive chemical and pharmacological studies have been performed only in the last few decades.
More than 20,000 species belong to bryophytes, comprising Marchantiophyta (liverworts, ~6000 species), Bryophyta (mosses, ~14,000 species), and Anthocerotophyta (hornworts, ~300 species), can be found everywhere in the world except in the sea. The Hungarian flora contains 659 species, with the predominance of mosses (2 hornworts, 146 liverworts, 511 mosses).
From phytochemical and pharmacological point of view, bryophytes are poorly explored because of the difficulties of their collection. Still high numbers of new compounds were discovered from mosses, including more than 40 new carbon skeletons of terpenoids and phenolic compounds. Mono-, sesqui-, di-, and triterpenes, flavonoids, bibenzyls, acetogenins are the most common types of secondary metabolites of bryophytes. These compounds show interesting biological activities, such as insecticide, insect antifeedant, cytotoxic, pesticide, muscle relaxant, plant growth regulator, anti-HIV, DNA polymerase β inhibitor, anti-obesity, neurotrophic, antioxidant, NO production inhibitor, antimicrobial, and antifungal activity.
Form a therapeutic point of view, the most perspective bioactivities of bryophytes are the anticancer and antibacterial effects. Several bryophyte crude extracts and isolated compounds were tested for cytotoxic activity on various cancer cell lines. Terpenoids and bibenzyls seems to be the most potent cytotoxic compounds as they may induce apoptosis by activating a number of genes and enzymes, however, the exact mechanism of action is still unknown. DNA fragmentation, nuclear condensation, activation of caspases, inhibition of anti-apoptotic nuclear transcriptional factor-kappaB, activation of p38 mitogen-activated protein kinase may play a role in apoptotic mechanism.
Liverworts are chemically different from mosses and hornworts because of the lack of oil bodies in the last two classes. In liverworts, the most common secondary metabolites are terpenoids, especially sesqui- and diterpenoids, from which more than 1600 compounds have been isolated over 40 years, however such compounds can be found in some mosses, including Mnium, Plagiomnium, Homalia, Plagiothecium and Taxiphyllum species and in hornworts includes Anthoceros species.
The first report of the antimicrobial effect of bryophytes was in published in 1942. In 1952 Madsen and Potes reported the antimicrobial effect of Sphagnum portoricense, Sphagnum strictum, Conocephalum conicum and Dumortiera hirsuta. In 1959, an examination where 12 species of bryophytes were tested showed the remarkable antibacterial effect of Anomodon rostratus, Orthotrichum rupestre and Mnium cuspidatum. A comprehensive study was published in 1979, where 52 species of bryophytes were tested on 8 bacterial strains; 56% of the tested species were active against at least one of the test bacteria.
However, most of the Hungarian bryophytes have not been examined phytochemically and pharmacologically. These species might be considered as an undiscovered and so far neglected corner of the (phyto)chemical space.