Phenology of reproductive shoots of eelgrass, Zostera marina L., at Roscoff (France)

Abstract

The development of flowering shoots and the maturation of flowers and fruits of Zostera marina L. were studied from May until the beginning of September 1978 at Roscoff (France) at two different tidal depths. Branches of flowering shoots matured acropetally, with the youngest branch as terminal inflorescence, and this also applied to the spathes within each branch. So, the development and maturation appeared to be a process starting at the base and proceeding to the apex of the shoot. Within spathes, the number of flowers varied greatly. A close examination of the first order spathes showed that the number of flowers per spathe was positively correlated with increasing tidal depth and branch number and negatively correlated with the initiation time of the spathes. However, the ratio of one pistil to one anther was always found, although at the apex of the spadix some anthers sometimes failed to mature. A direct relation between the number of flowers per spathe and the mean length of the spadix and the spatial sheath could not significantly be demonstrated. The mass flower production had already begun in the high-littoral bed in May, whereas this occureed in the lower bed one month later. However, the development and maturation of flowers and fruits occurred more quickly in the low-littoral bed than in the higher bed. As the ripening of fruits did not occur simultaneously, even within one spathe, this process could not be followed in situ.