If you go to the page for your image, say this one (and click through to "more photo details" if you're just getting the popup)
You will see a link near the bottom which says
Move this image to another plant
Click there. Then you will be prompted for the name of the plant you want to move it to. Pending approval (usually quickly) the change will be put into effect.
A second decision will need to be made regarding whether or not this variety called "Grandiflorus" exists, or is instead some kind of misnomer. Being no kind of expert I can only guess, but it sounds a little fishy. If the named plant should be deleted, that can also be done by a similar link ("delete this plant") near the bottom of the plant's page. Also pending admin approval.
