Development of each shoot of Echinodorus tenellus proceeds through a vegetative phase when foliage leaves are formed and enters an abruptly initiated reproductive phase, when only scale leaves are formed, by conversion of the meristem into a different form, while a large and precocious bud in the axil of the last foliage leaf continues vegetative development. The reproductive meristem may, according to conditions, form an inflorescence or a “pseudostolon” with vegetative axillary buds in place of flowers. Both inflorescence and pseudostolon show a regular sequence of long and short internodes and a regular alternation of scale leaves with and without axillary buds, though the pattern of the inflorescence is less regular than that of the pseudostolon and the inflorescence has a terminal flower while the pseudostolon has unlimited growth. Phyllotaxis varies according to the stage of development of the plant and in the reproductive shoot is largely determined by the patterns of internode elongation and bud distribution. The significance of the developmental pattern is discussed.