>Why do you suppose she named it that?

I've not read it; but I suspect this extract from the Ency. Brit. helps explain:
The tree was said to destroy all animal life within a radius of 15 m. or more. The poison was fetched by condemned malefactors, of whom scarcely two out of twenty returned. All this is pure fable, and in good part not even traditional fable, but mere invention.