Is Hypericum Perforatum (St. John's wort) a C3 or C4 plant? I've been curious as to which photosynthetic cycle St. John's wort uses to synthesise glucose and more complex carbohydrates. I know it probably won't be the crassulacean acid metabolism (CAM) cycle seeing how that applies mostly to plants that require a limited amount of water as opposed to St. John's wort which tends to prefer moisture. I suspect the answer to my question will be C3 seeing how they dominate in the plant kingdom and I know that St. John's wort requires relatively cool climates to grow successfully -- a trait characteristic of C3 plants seeing how high temperatures tend to cause excessive and wasteful photorespiration.

It's C3, according to the Illinois plant information network. (See CO₂ fixation on this page.) This is the best I could find.