MESOPHYLLUM-INCISUM (CORALLINACEAE, RHODOPHYTA) IN SOUTHERN AUSTRALIA - IMPLICATIONS FOR GENERIC AND SPECIFIC DELIMITATION IN THE MELOBESIOIDEAE

Detailed morphological, anatomical and systematic studies of southern Australian populations and the designated lectotype of Mesophyllum incisum (Corallinaceae, Rhodophyta) have shown that several growth-forms occur and the filamentous core in dorsiventrally organized parts of the thallus can vary from coaxial to noncoaxial. Spermatangia are simple and develop centripetally on the chamber floor and roof; initials are overlain by “protective” cells during early stages of development. One or possibly several independent fusion cells may develop within female conceptacles after karyogamy. Tetrasporangial conceptacles are initiated from filaments containing elongate subterminal cells, and pore canals of mature conceptacles are lined by distinctive cells that differ in shape from other roof cells. These results have led to a reconsideration of the delimitation of Mesophyllum as a genus and to differences between M. incisum and the type species, M. lichenoides. A description of the species is provided along with relevant nomenclatural, systematic and ecological data. © 1992, The British Phycological Society.