Currently (April 2020), the collection comprises 1184 cultivars, 184 landraces, 26 accessions of research material, 1033 samples of wild species and 108 accessions of unknown population type. The accessions of cultivated lettuce cover the seven generally recognized horticultural types, i.e. butterhead, cos, crisp, cutting, latin, stalk and oilseed lettuce.
In general, accessions of cultivated lettuce mainly originate from Europe, with the exception of crisp lettuce (USA), stalk lettuce (China) and oilseed lettuce (Egypt). Accessions of wild species are predominated by samples of L. saligna, L. virosa and particularly L. serriola. Accessions of wild species mainly originate from Europe and Asia. In 2008 the collection of cultivated lettuce was investigated for the presence of redundancies using passport, molecular and morphological data, after which nearly 200 accessions were removed (Van Treuren et al. 2010). Based on molecular data and a morphological field trial in 2010, 38 accessions of cultivated lettuce were discarded because of non-authenticity (Van de Wouw et al. 2011). In 2011, a redundancy analysis using passport and molecular data was carried out for the collection of wild species, resulting in the removal of 74 accessions. Improvement of collection composition will be continued with the periodical uptake of novel cultivars and with the organization of expeditions to thus far unexplored distribution regions of wild species that are considered useful in lettuce improvement. In this respect, expeditions have focussed on the collecting of L. serriola and L. georgica in the Trans Caucasus (2013), L. aculeata in Jordan (2017) and L. altaica and L. serriola in Uzbekistan (2019).
Seed samples from the two latter expeditions are not yet available for distribution.