Floral development of Hydrocleis nymphoides

Abstract

After the inception of three sepal primordia, three petal-stamen (CA) primordia (bulges) are formed in alternisepalous positions. On each of these bulges a petal is initiated, followed by a pair of stamens relatively high up on the bulge, where it is continuous with the floral apex. Growth extends between the three bulges, thus forming an inconspicuous circular rim around the floral apex. As this rim increases in size, further stamens and eventually staminodia are formed centrifugally on the rim. Five or six carpel primordia are initiated centrally to the first-formed pairs of stamen primordia long before all stamens and staminodia have appeared. In spite of considerable deviations from the trimerous monocotyledonous floral construction, the primary organogenetic pattern is trimerous (with the exception of at least the pentamerous flowers) and it is comparable to the primary patterns found in Alisma, Butomus, and other Alismatales. Thus, the study of the earliest developmental stages reveals a common plan that is elusive in later developmental stages and mature flowers.