Red algae, or Rhodophyta (/roʊˈdɒfɪtə/ roh-DOF-it-ə, /ˌroʊdəˈfaɪtə/ ROH-də-FY-tə; from Ancient Greek ῥόδον (rhodon), meaning 'rose', and φυτόν (phyton), meaning 'plant'), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority of species (6,793) are found in the Florideophyceae (class), and mostly consist of multicellular, marine algae, including many notable seaweeds. Approximately 5% of the red algae occur in freshwater environments with greater concentrations found in warmer areas. Except for two coastal cave dwelling species in the asexual class Cyanidiophyceae, that diverged from other red algae about 1. 3 billion years ago, there are no terrestrial species, which may be due to an evolutionary bottleneck where the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity.