The occurrence of branched and swollen rhizoids was investigated in 72–5 % of British hepatics (206 of the 284 species). Branched rhizoids are widespread in the Jungermanniales (100 of the 169 species) but are restricted to the Metzgeriineae in the Metzgeriales. They were not detected in the Marchantiidae. Terminal swellings, particularly well developed in the Lepidoziineae and Cephaloziineae, were found in 33 species in the Jungermanniales.
Rhizoid branching is associated with contact with a range of substrata whereas swollen rhizoids, exclusive to species growing on peat and rotten wood, are always associated with fungal hyphae. In some species, the hyphae probably derive from the fungal zone in the stem of the hepatic but, in others, they more likely come from repeated external invasions. The function of branched rhizoids is almost certainly anchorage whereas the swollen tips may well be absorbtive, probably involving the fungus as an intermediary.
Branched and swollen rhizoids are particularly prominent on flagellar shoots but are most developed on leafless underground stems. These hitherto undescribed subterranean axes which extend to depths of up to 20 cm in several members of the Lepidoziaceae and Cephaloziaceae may be important organs of perennation enabling plants to survive drought and fire.