Just over 600 species of non-vascular terrestrial plants have been identified in Iceland. The majority of these are mosses of class Bryopsida or liverworts of class Marchantiopsida. Hornworts are extremely rare in Iceland and found only in geothermal areas.
Hornworts (Anthocerotophyta) have irregular lobed or branching bodies, known as thalli, the tissue of which is not organised into organs. Guard cells form on the underside of the thallus. Cavities form under these that are typically filled with cyanobacteria. Only one species of hornwort has been found in Iceland, the Carolina hornwort (Phaeoceros carolinianus). Its distribution is confined to geothermal areas.
Liverworts (Marchantiophyta) are either made up of a thallus or leafy stems; unlike many mosses, liverwort leaves do not have ribs (costas). Around 140 liverwort species have been found here to date.
Mosses (Bryophyta) have thin stems around which simple leaves branch out. Moss leaves frequently have a midrib. A total of 460 moss species have been found in Iceland.
Non-vascular land plants in Iceland are similar to those found in northern Europe. The frequency of individual species varies by region. Three species of woolly fringed moss (Racomitrium lanuginosum, Racomitrium ericoides, and Racomitrium canescens) are among the most common plant species found in Iceland.
Mosses are more conspicuous in the Icelandic landscape than in many other geographic regions worldwide, and are the dominant species in many plant communities. The prevalence of mosses reflects various environmental factors, such as the climate and the repeated formation of new substrates, particularly lava fields. Heavy grazing by livestock has also hindered the growth of taller plants, allowing these shorter non-vascular plants to thrive.