In a locking element (5) for a fixing system (3) for quadrangular plate-shaped panels (1, 2) and comprising an insertion portion (6) for insertion into a locking groove (7) provided in the longitudinal direction of an edge of a first panel (1) and a locking portion (8) for engagement into a latching recess (10) of an undercut configuration provided in a laid configuration of the panels (1, 2) in an opposite edge of a second panel (2) and extending in the longitudinal direction of said edge and in opposite relationship to the locking groove (7), wherein the locking portion (8) includes a resilient latching tongue (9) which during assembly of the two panels (1, 2) is automatically latchable into the latching recess (10) into a latching position, the locking element (5) has anchoring means (18) and the locking element (5) can be captively anchored by the anchoring means (18) with its insertion portion (6) in the locking groove (7). The invention concerns also: a panel with holding profiles (4.1, 4.2) and an additional automatically latching locking element,- methods of locking quadrangular panels; and a method of automatically mounting a locking element to an edge of a panel well as an apparatus therefor.