Structure of long-tubed white corollas: A case study from the trumpet-creeper family (Bignoniaceae)

Abstract

Hawkmoth-pollinated plant species with white, long-tubed flowers have attracted the attention of scientists for a long time. However, most studies on these flowers have investigated their pollination biology, with only a few focusing on their anatomy. In this study, we conducted a detailed structural analysis of the long-tubed white flowers of Tanaecium jaroba Sw., a species from the “trumpet-creeper” family (Bignoniaceae). An in-depth understanding of the morphology of this flower type is critical for an accurate interpretation of the evolution of this structure. We found that the long floral tube develops as a result of intercalary growth; no increment of number in the flower whorls were observed. We documented osmophores on the apices of the corolla tube for the first time for the family Bignoniaceae. In addition, studies on the vasculature showed a secondary division of the ovary into two locules due to the inward growth and merging of the parietal placentae, forming a placental lamella. Our study highlights the importance of detailed morphological and anatomical studies at lower taxonomic levels, establishing the basis for future studies on the evolution of flower morphology in Bignonieae, and the Bignoniaceae as a whole.