Periploca angustifolia Labill., is a multipurpose shrub also used to rehabilitate drylands. It is essential to understand its phenological patterns under arid conditions. In order to understand how plants manage extreme drought, this study investigates the relationship between phenological traits of P. angustifolia Labill., water potential and climatic conditions. During two successive growing seasons (Sep 2009-Augst 2011) phenological patterns, soil water content and water potentials were measured monthly for plants of Periploca angustifolia Labill growing under rain-fed conditions (Annual rainfall = 168 mm) at the pastoretum of the Arid Regions Institute in southern Tunisia. The psi md decreased progressively and concomitantly with increasing seasonal drought, reaching the lowest values in late summer (down to -3 MPa). Water potentials of P. angustifolia Labill were affected by spatial and temporal variations in soil water content. The increased diurnal amplitude values ( increment psi > -1.3 MPa) explained the especially high biological activity of this species during the dry season. Our results clearly demonstrate that P. angustifolia Labill is a drought-tolerant species reaching low water potentials during the driest months of summer. These characteristics make this shrub as promising for rehabilitating degraded arid ecosystems.