Functional Stomata of the Atmospheric Epiphyte Tillandsia usneoides L.

Although stomatal opening in Tillandsia usneoides is not detectable by light microscopy, the guard cells swell in the dark and in the light in buffers known to stimulate stomatal opening. Abscisic acid or phenylmercuric acetate substantially reduced subsequent nocturnal CO2 uptake. Potassium ions were more concentrated in the guard cells in the dark than in the light. The stomata of this CAM epiphyte appear functional: open at night and closed throughout most of the day.