Embryo to seed length ratio and embryo to seed surface ratio data

To demonstrate the bias of data availability towards non-tropical species, we compiled data on embryo length to seed length ratio and embryo to seed surface ratio for 1295 spermatophyte species. These data were obtained mainly from pictures or drawings available in the main literature sources dealing with the internal morphology of seeds (e.g., Martin, 1946; RBG Kew, 2021 [SID]; Watson & Dallwitz, 1992) and from measurements on living material (Vandelook et al., 2012; Vandelook et al., 2021). Care was taken that the measurements were taken on transversal sections of seeds at the moment of ripeness, which had maximal embryo surface area. The embryo to seed length ratio was calculated by measuring total embryo length and dividing this by the length of the seed, measured from the inside of the seed coat, along the longest axis. The embryo to seed surface area was calculated by dividing the embryo area by the area of the embryo plus endosperm and perisperm. In case of curved or coiled embryos, the lengths of different segments were summed. All occurrence coordinates for these species were downloaded from GBIF (GBIF download DOI:10.15468/dl.mat4zv). Using these coordinates, we calculated the percentage of occurrences in the tropics (between the Tropic of Cancer and the Tropic of Capricorn) and outside of the tropics for each species. Duplicate coordinates within a species were removed prior to calculation.