| Abstract: | The floral organogenesis of Potamogeton distinctus A. Benn. was observed under the
scanning electron microscope (SEM). The floral buds are first initiated on the lower portion of inflorescence in alternating whorls of three. Each of the floral buds is subtended by a bract primordium
during the early stages. The primordia of the floral appendages arise on the floral bud acropetally.
Two lateral tepals are first initiated and then two median ones soon after. Stamens are normally initiated as elongate primordia opposite the tepals, with the two lateral stamens preceding the median
ones. The two carpel primordia arise alternating with the stamens. In some flowers, one of the two
gynoecial primordia becomes inactive soon after they are initiated, or only one carpel primordium is
initiated. The present observation of the gynoecial development supports the viewpoint that the evolution of flower in Potamogeton involves a reduction in number of parts. The existence of bract primordium during the early stages in many species of Potamogeton indicates that the absence of bractin mature flowers should be the result of reduction. |
