"vertebrata thuyoides" is a small marine algae growing to 15 cm high in dense tufts of erect branches borne alternately and in one plane. the erect branches have 8 to 10 pericentral cells surrounding the central axis and are all of the same length. the whole plant is corticated, and is attached by rhizoids. it is very similar to "vertebrata fruticulosa". "pterosiphonia complanata" is similar but can be distinguished by having 5 pericentral around the central cells of the axes.