Floral humidity in flowering plants: a preliminary survey

The area of space immediately around the floral display is likely to have an increased level of humidity relative to the environment around it, due to both nectar evaporation and floral transpiration. This increased level of floral humidity could act as a close-distance cue for pollinators. However, with a few exceptions, not much is known about the patterns of floral humidity in flowering plants. We conducted a survey of 42 radially-symmetrical flower species (representing 21 widely-spread families) under controlled conditions. Humidity was measured using a novel robot arm technique that allowed us to take measurements along transects across and above the floral surface. Thirty of the species we surveyed presented levels of humidity exceeding a control comparable to background humidity levels. Patterns of floral humidity differed across species. Nevertheless, floral humidity tended to be highest near the centre of the flower, and decreased logarithmically with increasing distance above the flower. These results demonstrate that floral humidity may be produced by a wide range of species. In addition to physiological traits, shape seems to influence the diversity of measured humidity patterns. There might be greater level of complexity in this floral trait than previously known.