Morphological and anatomical development in the Vitaceae. VII. Floral development in Rhoicissus digitata with respect to other genera in the family

This study forms part of our series of investigations on genera in the Vitaceae and is the first developmental study for the genus Rhoicissus. Vegetative and reproductive development of shoot apices of Rhoicissus digitata (L.f.) Gilg et Brandt were examined using epi-illumination light microscopy and scanning electron microscopy. Leaf-opposed tendrils or inflorescences, typical of the shoot architecture in the Vitaceae, were present at every node. Macroscopically, the shoot appears to grow either monopodially or sympodially. At the microscopic level, however, shoot development is sympodial; the shoot apical meristem bifurcates unequally, with the larger portion forming an uncommitted primordium, which will become either an inflorescence or a tendril, and the smaller portion (in the position of the axillary bud) forming the new shoot apical meristem. Floral primordia first initiate three sepals followed by a calyx ring on which the last two sepal primordia form. The five petals are initiated in a whorl followed by the five stamens in a petal-opposed position. There is no evidence of a common petal-stamen primordium in this species. The gy noecium is initiated as a ring primordium. Subsequently, the four ovules are initiated at the base of the two septa that grow out from the inner gynoecial wall. The nectary disc forms as an outgrowth of the gynoecium base. Mature flowers have greenish petals and a red nectariferous disc. Flowers are bisexual, and seed germination is approximately 63%. Unlike previous studies in Vitis and Parthenocissus, Rhoicissus appears to have few putatively derived floral developmental characters, which would support its relatively basal position in current phylogenies for the family.Key words: Vitaceae, morphology, development, shoot architecture, flower.