Hello.
Thanks for providing code , but you could take further steps to make it more convenient for other forum users to help you. Share some representative data that will enable your code to run and show the problematic behaviour. You might use tools such as the library datapasta, or the base function dput() to share a portion of data in code form, i.e. that can be copied from forum and pasted to R session. Reprex Guide
If I were to guess what's going on; I don't see the three extra rows per plant species. Note there are multiple distinct values of weight/grams per plot for each plant + treatment /ounces per plot combination.