Floating aquatics, members of the family are characterized by the most complex reproductive structures of any known plant.
SORI are short-stalked, and borne on the lower of the two leaf lobes.
The megaspore has an accessory structure, the columella, which bears floats. The microspores are embedded in massulae, which have projecting structures called glochidia on their outer surface. Usually bearing short roots, they are indurated, and sometimes also have trichomes. The upper lobe is usually palpillate, without veins. Anabaena is also able to fix its own nitrogen.