Frerea indica, a stem succulent CAM plant with deciduous C3 leaves.

Abstract

During the winter in greenhouse culture, Frerea indica(Asclepiadaceae) is a leafless stem succulent resembling the other members of the Stapelieae subfamily. However, in spring it produces leaves which persist during the summer period. CO2 exchange measurements were carried out with Frerea indica at its different seasonal states of development. The leafless stems in winter as well as the defoliated ones in summer show all characteristics of Crassulacean acid metabolism. The leaves, on the other hand, fix CO2 with high rates according to the C3 pathway; no diurnal malate fluctuations are detectable. This feature can be interpreted as an ecological adaptation where a seasonal plant dimorphism enables a functional change in the prevailing mode of CO2 metabolism. In the leafless state, which probably represents the appearance of the plant during the dry period in nature, it is saving water by pursuing CAM. The season with enough water available can be used for high photosynthetic gain by C3 leaves.