Nodding capitula in superparamo Asteraceae: an adaptation to unpredictable environment

Nodding capitula are a striking feature in several Asteraceae species of the Andean superparamo. In this study, the thermal environment of the nodding inflorescence in Culcitium canescens Humb. & Bonpl. was surveyed by a short-term microclimatic measurement. Temperatures of the nodding inflorescences were higher than temperatures of the surrounding air during the day, while the respective temperatures were comparable during the night. Also, compared to other parts of the plant, the nodding inflorescence provided favorable temperature conditions. An experiment showed that the radiation reflected from the substratum explained most of the variability in the inflorescence temperature. It is suggested that the nodding capitula have evolved to protect the flowers from snow and rain while at the same time ensuring sufficient temperatures for floral development.