Cal double dagger ots are the immature floral stems of second-year resprouts of the 'Blanca Tardana de Lleida' (BTL) onion landrace, and to date, breeding has used only a few populations. So, we aimed to increase our knowledge of the variability of BTL and to explore its characteristics and genetic dissimilarity with other varieties that might be used in cal double dagger ot breeding programs. We analyzed the agronomic and morphological traits of four populations of BTL, two synthetic varieties of BTL, 20 prestigious Spanish landraces, and 4 exotic onion landraces. Furthermore, we used three combinations of AFLP primers and seven microsatellites to analyze their genetic background. The Spanish landraces (including BTL) shared a large part of their genetic background, which showed considerable variability (heterozygosity around 0.5). Morphological traits also had high variability, so multiple breeding strategies can be used, ranging from intravarietal selection to crossings between populations to take advantage of the heterosis, both for the bulb and for the cal double dagger ot improvement.