My hope for categories going forward is to have fewer categories, and more general ones, not more specific. After all, there are thousands of different kinds of flowers, plants and trees.
I don't think, for example, that a picture of a Salvia flower needs to only be judged against another Salvia. I think a rose bush picture can be judged against a buddleia bush picture. A garden scene from Seattle can be judged against one from Florida, even though the plants are very different. Here's why:
Since it's a Photo Contest, we are supposed to vote on the merits of the picture itself, not the subject matter. Composition, lighting, framing, angle, originality . . . so many other factors make a great photo, but not necessarily the flower, plant or tree, bug or animal in the picture.
For example, I spent a ton of time on the Daylilies forum the last few months. The flowers are absolutely stunning, and the array of colors, forms, markings, sizes and shapes is mind-boggling. But most of the excellent pictures on that forum are geared towards showing the details of the flower so they are well lit, full frame, flower face to the camera. To me those aren't the kind of photos you would enter in a photo contest. They'd be impossible to judge because even though the flowers are different, the photos are too similar. A whole clump of Daylilies is a more apt subject because it gives scope to the photographer's talent.
Thus, you'd be better to put Daylilies in a "Perennials" or "Single plant" category and then a daylily clump picture could be judged against a clump of . . . Cannas? Daisies? Salvias? Agastaches?