1) Fictional shapeshifter 2) Plant disease 3) The tree bearing this fruit 
[plant disease] Blackheart is a non-parasitic disease of the fruit of cultivated plants, such as tomatoes, that causes them to rot from the inside. External signs of the disease may or may not be present. The internal blackening develops in plants exposed to environmental pathology such as drought conditions or poor soil. == Blossom-end rot...
• (n.) A heart-shaped cherry with a very dark-colored skin.
Black'heart` noun A heart-shaped cherry with a very dark-colored skin. 
[n] - any of various diseases in which the central tissues blacken 2. [n] - heart cherry with dark flesh and skin cherry
blackheart cherry noun heart cherry with dark flesh and skin cherry
a nonparasitic disease of plants, as of potatoes and various trees, in which internal plant tissues blacken, usually as a result of extremes in temperature. · · a heart cherry having a dark skin. · the tree bearing this fruit.