It doesn't have to necessarily be that Grandpa longneck is sick again, but he could be the one who gives the quest since he may have heard another resident is sick and needs some night flowers. Would also kinda make sense since the quest may be given to different folks over time. Since the dinos don't seem to have the mentality of, let's get extra and store some here, or see if it has seeds, see if we can grow some here in the swampy parts of the Great Valley.