Floral ontogeny and anatomy in Koelreuteria with special emphasis on monosymmetry and septal cavities

The floral ontogeny and anatomy of Koelreuteria paniculata have been invest igated to understand the developmental basis for the occurring monosymmetry and the origin of the septal cavities. Petals arise sequentially and one p etal is missing between sepals 3 and 5, or rarely between sepals 2 and 5. T he eight stamens arise sequentially before petal initiation is completed. T he last formed petal and one stamen arise on a common primordium. Two stame n positions are empty (opposite the petal between the sepals 2 and 5, and t he petal between sepal 1 and 3), consequently two antesepalous stamens have become displaced. The derivation of octandry from a diplostemonous ancestr y, and reduction of the petal are discussed. The triangular gynoecium has a strong impact in obliquely reorganizing the symmetry of the flower, loss o f organs, and shifts of stamens. The so-called septal slits occurring withi n the style are a deep-reaching non-nectariferous extension of the stigma. Alternating locular furrows are present which could play a role as pollen t ransmitting tissue and in the loculicid dehiscence of the capsule.