The Garden of Death and Healing

Poisonous Plants:
Aconite/Wolfsbane
Belladonna (Nightshade)
Foxglove
Hemlock
Iocaine/Iocane
Nightbane (A hallucinogen poison that causes its victim to experience increasingly horrible nightmares every time they sleep until an antidote is administered.)
Oleander
 Scarlet Pimpernel -
Gympie Gympie plant - Dendrocnide moroides, commonly known in Australia as the stinging tree, stinging bush, or gympie-gympie, is a plant in the nettle family Urticaceae found in rainforest areas of Malaysia and Australia.[3] It is notorious for its extremely painful and long-lasting sting. The common name gympie-gympie comes from the language of the indigenous Gubbi Gubbi people of south-eastern Queensland.

Plants
Baronel (brown flower with yellow spots. Toxic when young and the flowers haven't fully bloomed. Beneficial when the flowers not only bloom but have yellow spots.)
Cardassian Taroberries (small plant with bright green berries that cause fever)
Jewel fruit (The root of the jewel fruit has medicinal properties, but the flowers are toxic)
Herbs:
Aloe Vera
Chamomile
Fever few
St John's Wort

Both Poisons and Healing
Opium Poppy plants (makes morphine and heroin)
Erythroxylum coca (The Coco plant that makes Cocaine)