You want to use numbers instead of genus and species as your plant codes in your planting labels / callouts.
You can use numbers in this way, but it's not recommended. Here's how to do it:
In the Planting Preferences, you can choose the default code style GEN SPE or GS, correlating with either a two- or seven-character code. Regardless of which code any plant has, you can always change it to meet your preferences.
Keep in mind that using numbers as a code is highly nonstandard, and not recommended. If you use numbers as plant codes, they can easily be confused with plant quantities.
For more information on customizing plant labels, see our Create New Plant Label Styles documentation.