I like the technique of testing if it was carnivorous. For the lazy people, they put a nitrogen isotope inside fruitflies and then tested the plant later to see if it was absorbing the nitrogen, and it was.
Their spines all point towards the base of the plant, where, in a mature specimen, there’s usually a hollow without thorns.
Thing is, if you’re a furry or woolly animal, like a sheep, and you get caught in the thorns, your struggles bring you into the centre of the plant, where you’re thoroughly trapped, and you die of exhaustion.
Then you decompose, and the bramble gets fed.
I’ve seen this happen to sheep, and here, while clearing huge swathes of giant brambles, it’s not uncommon to find a skull or a few bits of bone around the bottom of a plant.
The plant in the article is less ambiguous: they detected a digestive enzyme in the sticky stalks which is common to other carnivorous plants, and means the plant digests the insects directly.
A bramble consumes unlucky mammals with the help of mycorrhisae in the soil, rather doing so directly. Is this more like the bacteria which help ruminants digest cellulose (no one would say that cows don't eat grass!) or is it more like saying that vegans are carnivores because organic fertilizers have blood and fish meal in them?
If it absorbs half it's nitrogen from insects that get stuck to the stem…