Ecophysiological responses of homoiochlorophyllous and poikilochlorophyllous desiccation tolerant plants: a comparison and an ecological perspective

There is an apparently stark contrast in ecophysiological adaptation between the poikilochlorophyllous desiccation-tolerant (PDT) angiosperm Xerophyta scabrida and homoichlorophyllous desiccation-tolerant (HDT) lichens and bryophytes. We summarise measurements on Xerophyta and on the temperate dry-grassland lichen Cladonia convoluta and the moss Tortula ruralis through a cycle of desiccation and rehydration. Considered in a broad ecological and evolutionary context, desiccation tolerance in general can be seen as evading some of the usual problems of drought stress, and these plants as particular instances drawn from an essentially continuous spectrum of adaptive possibilities - related on the one hand to the physical scale of the plants, and on the other to the time-scale of wetting and drying episodes.