Vegetative and reproductive development of Halarachnion ligulatum (Gigartinales, Rhodophyta)

Abstract

The vegetative and reproductive development of Halarachnion ligulatum has been investigated using haematoxylin stain and Differential Interference Contrast microscopy. Growth is multiaxial, initiated by five to seven apical cells. Each axial cell bears a single determinate lateral that forms the two-layered cortex and medulla. Rhizoids traverse the thallus and terminate by wedging between cells of the opposite cortical layer. Secondary pit connections are absent. Auxiliary cells are cytologically modified and are distinguishable by the number of laterals they bear. Connecting filaments and auxiliary cells exhibit a specific interactive behaviour prior to fusion and gonimoblast initiation. These observations are discussed with reference to the diagnosis and circumscription of the Furcellariaceae and its relationship to the Nemastomataceae and Solieriaceae of the Gigartinales.