Plants of the largest species can reach 60 cm in length. Thalli range from erect to prostrate and from terete to broadly flattened. Some species form articulated fronds composed of cylindrical or irregularly shaped units. The apical structure of the type species has been demonstrated by Kling & Bodard (1986) to be uniaxial, although too compact to be easily interpreted. Procarps, fusion-cell formation, and early gonimoblast development are typical of the family. In most species, nutrient tubular cells connect the gonimoblast to cells of the inner pericarp. Carposporangia occur in chains, and cystocarps are strongly protuberant. Spermatangia have been reported to form in one of 3 taxonomically important patterns (Bird and McLachlan 1984), either as a completely superficial continuum or in sori flush with the outer cortex ("Chorda"-type), in shallow sunken patches ("Textorii"-type), or in deep conceptacular pits ("Verrucosa"-type). Fredericq and Hommersand (1989b) have advocated removal of species with the "Chorda"-type spermatangia to the genus Gracilariopsis (see below). Tetrasporangia are mostly decussate-cruciate and occur both scattered and in nemathecia, according to the species.