A Floral Ontogenetic Study in the Dipsacales

Abstract

The floral ontogeny of five representative species (Lonicera periclymenum, Symphoricarpos albus, Centranthus ruber, Dipsacus sylvestris, and Knautia arvensis) of Dipsacales has been studied and compared with existing floral ontogenies in order to examine the unresolved systematic position of Dipsacales. The floral ontogeny of the species studied differs only in minor aspects. All inflorescences share a basic dichotomous branching pattern initiated in an acropetal direction. The flowers of Dipsacus and Knautia (Dipsacaceae) arise successively in contact parastichies and are grouped in heads. However, the earliest flowers in the heads of Dipsacus are initiated in pairs, making a connection with the other dipsacalean families possible. In Dipsacaceae an epicalyx with a mixed bract and bracteolar origin arises. The sepals arise as individual primordia in Lonicera and Symphoricarpos (Caprifoliaceae). In the other genera individual sepal primordia are not observed, but a sepaloid meristematic ring is formed instead. The petal primordia are initiated on a meristematic ringlike zone on the floral apex. A reductive trend is seen in the androecium. The number of stamens and/or their fertility is reduced from the adaxial to the abaxial part of the flower; however, the direction of the reduction can be reversed. The first step in gynoecium development is the initiation of a central depression in the floral apex. Individual carpel primordia are never observed. The gynoecia of Centranthus (Valerianaceae), Dipsacus, and Knautia are extremely reduced. Comparison of the floral ontogenies of Apiales, Asterales-Campanulales, and Dipsacales reveals a high degree of similarity.