Unrecorded liverwort species from Korean flora V: New data on Riccia (Marchantiophyta) from Korean Islands

During a floristic survey of coastal and island regions of Korea, we identified two previously unrecorded species of the genus Riccia L. (Ricciaceae): Riccia cavernosa Hoffm. and R. nipponica S. Hatt. R. cavernosa, originally described from Germany and widely distributed across the Holarctic region, was newly confirmed in Korea from Gyodongdo Island (Incheon) and Gangneung (Gangwon-do). R. nipponica, previously known from Japan, China, and the Russian Far East, was newly discovered on Jeju-do, typically inhabiting moist soils in rice-field habitats. Detailed morphological descriptions, illustrations, and diagnostic characters distinguishing these taxa from morphologically similar Korean species, in this case R. huebeneriana and R. glauca, are provided. These results highlight the importance of continuous bryofloristic investigations, particularly in underexplored habitats such as islands and agricultural wetlands, for a more comprehensive understanding of the liverwort flora of Korea.