Carbon is carbon is carbon

I am reading a book called "the greatest show on earth" by Richard Dawkins, and there is a sentence that goes

"To a plant, carbon is carbon is carbon."

Here I don't understand the grammar and I haven't come across a sentence like this before. What confuses me is the two consecutive "is"s without a relative pronoun. What is this structure called and what does the sentence mean? And can you also give an example of your own if possible?

Thanks!