Tank-inflorescence in Nidularium innocentii (Bromeliaceae): three-dimensional model and development

Abstract In Nidularium, inflorescence branches are subtended by large floral bracts, in which water accumulates. The branching pattern is obscured because their internodes remain short, hampering their interpretation. This study focuses on the development of the inflorescence in N. innocentii, combining different approaches in order to understand its architecture and summarize it in a three-dimensional (3D) model. We also present the interpretation of tank-inflorescence development, recognizing the processes that have taken place in the evolution of this structure in this group. The inflorescence was typified based on Troll’s and Weberling’s systems. Development was studied using light microscopy and X-ray microcomputed tomography. The system is polytelic; the main axis ends in the main florescence and bears lateral paraclades with coflorescences. Each lateral branch develops in the axil of a bract, which is large and displays alternate arrangement. No prophylls were observed in the system. In the 3D reconstruction, the volume of the model was calculated. The volume of the empty region is c. 2.4 times higher than the plant material. Tank-inflorescence development seems to have occurred by the combination of three processes: bract disposition and its overgrowth; failure in internode elongation; and paraclade flattening. The tank-inflorescence evolved in a few groups of core bromelioids, and may be associated with floral protection.