COENOGONIUM: A GREEN ALGAL LICHEN WITHOUT PHOTOSYNTHETIC DEPRESSION AT HIGH WATER CONTENTS

For experiments run at 350 ppm CO₂, the subtropical lichenCoenogoniumdoes not exhibit net photosynthetic depression at water contents above those at which initial maximal values are reached. This is in contrast to most lichens for which such a depression occurs. We infer that the results reflect the unusual morphology ofCoenogonium, in which the alga is the dominant symbiont, occurring as filaments at the lichen surface. This arrangement should minimize CO₂diffusion resistance to the algal surface. With light saturation occurring by 70 μmol photons m⁻²s⁻¹,Coenogoniiumhas one of the lowest light saturation values reported among lichens.