The moderators and admins have the ability to choose a particular photo to serve as the main thumbnail image for a plant. I don't know why it was done in this case, but we had a couple of reasons to do it in the rose database. Before there was anything like a thumbs-up, the thumbnail was always the first image uploaded to the entry, but subsequent images often were more representative or of better quality, so we would choose one of them to serve as the main thumbnail. After the thumbs-up feature was instituted, the photo gaining the most thumbs-ups was not necessarily better than an older image that had not been eligible for a thumbs-up at the start and had not gained enough attention simply by appearing occasionally as the random plant image.
