The degenerative plant parts which are not useful for any processes are

The degenerative plant parts which are not useful for any processes are vestigial structures.
Vestigiality or vestigial structures are the retentions, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species.
Plants also have vestigial parts, including functionless stipules and carpels, leaf reduction of Equisetum, and paraphyses of Fungi.