For over eighty years, intriguing Lathyrus populations have been observed in Belgium along railways and wastelands, with the earliest herbarium material from 1943, 1955, and 1978, all collected near Antwerp. They resemble L. sylvestris but have broader leaflets that are rounded at the apex, wider stipules, and more robust stem wings.Recent genetic analyses demonstrate that these Belgian populations represent a distinct species, Lathyrus platyphyllos, closely related to L. sylvestris but forming a genetically distinct lineage, clearly separate from L. sylvestris, L. latifolius, and L. heterophyllus. In the field, L. platyphyllos can be reliably identified by leaf shape and width, stipules, stem wings, flower size and colour, the length of the seed hilum, and the distance over which the style is hairy from its tip. Correct identification allows for a more precise understanding of its distribution and supports ecological studies.