Palaeobiogeographic patterns of a persistent monophyletic lineage: Lithophyllum pustulatum species group (Corallinaceae, Corallinales, Rhodophyta)

The Lithophyllum pustulatum (Lamouroux) Foslie species group (Corallinaceae, Corallinales, Rhodophyta) includes those species of Lithophyllum in which plants have a dimerous, dorsiventral internal organization with primigenous filaments composed of palisade cells and in which floors of functional tetra/bisporangial conceptacles are one to three cell layers below the surrounding vegetative thallus surface. Several extant species have been recorded in shallow-water settings in the Mediterranean Sea, in the Atlantic, in the Indian, and in the Pacific oceans. In addition to its widespread geographic occurrence, the L. pustulatum species group has a long geological record which can be traced to the Late Oligocene. Analysis of data from the palaeontological literature, combined with the study of both fossil and living samples, shows that present-day populations of the L. pustulatum species group derive from Late Oligocene ancestors in the Pacific as the oldest-known records of the group are from Upper Oligocene shallow-water carbonates from Ko{combining overline}ko Seamount in the central Pacific Ocean. Early Miocene migrants arrived in the eastern Pacific, including at that time the Caribbean region, and in the Zagros Basin in Iran. Before the Langhian closure of the connection between the Mediterranean Sea and the Indian Ocean, the species group reached the Mediterranean area. Within the Mediterranean, the group migrated westwards during the Middle and Late Miocene and, subsequently, colonized the eastern Atlantic. This long dispersal history (more than 27 million years) might explain the broad present-day distribution of the species group across diverse environmental gradients and geographical barriers.