Many genera of this family have seeds equipped with elaiosomes, adapted to dispersal by ants (myrmecochory). Most often they are very attractive, and not only for ants ;) To note that they are ‘visible’ only while the seeds are fresh. Even when the seeds are kept on moist storage, the appendices will quickly disappear (see insert for Stylophorum diphyllum). So, for some species where the pictures were taken later, the elaiosomes are not presented.

Other genera, exemplified here by Meconopsis, Papaver and Glaucium, do not present elaiosomes and in general have small size seeds.
Hover to see the names; click to open full size images.