In the Mar Piccolo of Taranto (southern Italy, Mediterranean Sea), an enclosed basin with lagoonal features, Acanthophora nayadiformis is one of the major components of the free-living seaweed community to which the related attached population does not contribute consistently. Loose thalli of A. nayadiformis exhibit morphological features very different from those of the attached specimens and possess a peculiar vegetative cycle including an overwintering phase. Free-living morphs are characterized by monopodial stoloniferous growth; in contrast, both determinate and indeterminate branching as well as the typical ramisympodial growth pattern of the species are lacking. In autumn, free-living thalli fragment giving rise to stolon pieces which undergo deep structural changes in their sub-apical parts including both storage of floridean starch and extensive cortical thickening. Soon afterwards the uncorticated parts decay, whilst the modified fragments are able to overwinter and give rise to new fronds during next spring.