Carpellary and Placental Structure in the Solanaceae

Abstract

The floral anatomy of fourteen genera and twenty-one species of the Solanaceae was examined. The arrangement of the genera is according to Wettstein in Engler and Prantl's Die Naturlichen Pflanzenfamilien. In the order of their complexity, these genera include Nicandra, Lycium, Atropa, Hyoscyamus, Physalis, Capsicum, Solanum, Lycopersicon, Datura, Nicotiana, Petunia, Nierembergia, Salpiglossis, and Schizanthus. The following evolutionary tendencies were noted: actinomorphy to zygomorphy; reduction of fertile stamens from five to two; and reduction in the number of adaxial bundles from two per carpel to one for two carpels. Despite these variations, the floral anatomy follows the same basic plan in all the species studied. The siphonostele generally becomes continuous after the divergences to each of the first three floral sets, and the carpellary bundles are formed from the remaining vascular tissue. Because the adaxial bundles are amphicribral and accompanied by gaps in the vascular cylinder, they are foliar rather than cauline. The placentae are axile in position, while the carpel walls, the septa, and the ovule-bearing portions of the placentae are foliar in origin. The central parenchymatous part of the ovary is stelar, and the carpels are undiverged leaves.