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Calligonum azel, C comosum and C arich (Polygonaceae) are three dominant and economically important species widely distributed in active sand duties in the Southern desert of Tunisia, which differ in growth form and may co-occur under the same climatic constraints. The aims of this work were to compare their phenological and water potential patterns, as well as branch, flower and fruit production during three years at monthly intervals. Predawn (Psi(pd)) and midday (Psi(md)) water potentials followed similar trends with a few exceptions. For all species, reached values more negative than -2.5 MPa during the hot and dry summer, with extremes in July Psi(pd) differed between the species, and C. comosum attained the most negative values (-1 71 MPa) Seasonal differences in Psi(pd) were less pronounced for Calligonum species established in duties its compared to C comosum from interdunes. Spatial and temporal variations in soil water content provoked changes in water potentials of these species. Diurnal amplitudes resulting from the difference between Psi(md) and Psi(pd) were more pronounced during the dry season compared to the wet months. The phenological pattern of the three species showed it similar sequence of phenophases with growth activity Occurring mostly between spring and summer. We found species-dependent response to summer drought, as C. comosum ended all phenophases in June, while C. azel and C. arich extended their vegetative growth into the summer period of low precipitation. Water availability for the plants was better on the dune slopes. Differences were statistically significant along species, concerning green branch production and numbers of initially Formed flowers and Mature fruits Our data suggest that changes in the studied parameters may depend oil the rooting depth of the species. (C) 2009 Elsevier GmbH. All rights reserved.