The ID numbers for the "child" entries are in a box on the top right, but the ID numbers for parent plants are at the bottom of the page.
If you enter Fuchsia in the database search box, you'll be taken to a page where you can choose to go to the parent plant or to browse all of the plants in the Fuchsia genus.
http://garden.org/plants/searc...
Click on the parent plant link and you'll be taken to this page, with the ID number at the bottom.
Fuchsias (Fuchsia)
