Staple (1) for tying a plant stem or branch to a guide element (8), string or similar, where the staple (1) is formed of a thin metal rod, bent until it presents a specific form that enables an independent clamping of the guide element (8) and of the branch, with the advantage that the design of the staple (1) is valid for applications with guide elements (8) of different thicknesses or diameters, from tapes or thin strings to thick strings and even poles. To achieve this, the staple (1, 1') presents a convex projection (4, 4') formed on its central part (3) and which may present various sizes. An interior cavity (6, 6') located in the convex projection (4, 4') may remain or not when the staple (1, 1') is closed.