Morphology of Acanthophora nayadiformis (Ceramiales, Rhodophyta)

Acanthophora nayadiformis is a perennial species of red alga that overwinters by means of a rhizomatous prostrate system; both reproductive and vegetative plants are also able to spread by means of specialized vegetative propagules that have never been reported in other Acanthophora species. A detailed study of thallus morphology has highlighted four kinds of primordia in this species, distinct in shape, size and origin, that develop into as many different types of branches. Thallus growth is at first monopodial, shifting to ramisympodial in most plants. Even the morphological variation observed among tetrasporiferous branches is caused by the type and development of their parent primordia, which confirms the extreme inadequacy of this feature for taxonomic or diagnostic use at species level.