A rotor including blades rotating around a rotation axis (X), each blade being configured to transmit to the rotation axis, during a revolution of the rotor around the rotation axis, under the effect of the flow of a fluid, alternately a driving torque that rotates the rotor, and a resistant torque tending to go against the rotation of the rotor, each blade including in a region of an outer longitudinal edge of the blade, a flexible part configured to retract towards the inside of the rotor, when the blade transmits the resistant torque to the rotation axis of the rotor, and to switch to a position extended towards the outside of the rotor, during the rotor half-revolution following a maximum retraction position, when the blade transmits the driving torque to the rotation axis of the rotor, the flexible part being driven only under the effect of the flow of the fluid.