The flowering of Zostera marina was studied in a shallow meadow in the
Venice lagoon (North Adriatic Sea) in spring and summer 1995. Vegetat
ive and fertile shoot density and size were recorded during the flower
ing period. Spathe maturation was divided in six phases according to d
ifferent stages of anthesis. New spathes were first observed in Februa
ry and anther and pistil maturation proceeded until March. The beginni
ng of anthesis, with styles erecting, occurred in April while fruits a
ppeared in May and June. A statistically significant difference betwee
n fertile and vegetative shoot height was found for all months. The st
art of flowering (February-March) appears to be early in the Venice la
goon in comparison to Atlantic European sites, where it starts from Ju
ne onward. A six-month long flowering period is one of the longest obs
erved. The estimated potential seed production seems limited if compar
ed with the values relative to North European and North American coast
s.