I wrote the creator who was kind and gracious enough to answer some questions.
The Empress is a Pomegranate. Egad, I'm worse at plant ID then I thought because I thought this
should be a pomegranate...I mean what else? And the Devil is Hemlock, Belladonna, and Oleander.
And here about a the possibility of creating a book that identifies the plants:
"I designed the Ophidia Rosa to be an intuitive Tarot, for the poems in the foldout to correlate directly to the illustrations and provide an extra layer of meaning to the cards. To evoke feelings and shed light, but also to keep the mystery of the Tarot intact -- within that mystery, is where I believe so much magic lives."
She said that there are cards with flowers and plants that crossover with the Pythia Botanica Oracle, so if you want to research you can find the meanings there. I feel better after reading her email and think I'm going to familiarize myself with the Oracle first, then move onto the Tarot. It seems like a natural progression as she created the PBOracle first in any case.
She also mysteriously mentions she is working on something else related to the Ophidia Rosa Tarot. So we shall see that in the future.