I think Bellatrix would be Digitalis (Foxglove). Digitalis is a plant that is poisonous and can cause hallucinations and delusions. Since Bellatrix is basically insane, it makes sense to associate her with a plant that can cause mind altering effects. However, digitalis can also be used medicinally, which is fitting to Bellatrix because she is so unpredictable, and can respond to things in different ways. Furthermore, digitalis frequently grows in areas where the ground has recently been disturbed, most commonly burned, which makes sense since Bellatrix thrives on chaos and disaster.

Tasha//Gryffindor