May apple

1. A rhizomatous plant (Podophyllum peltatum) of eastern North America, having a single, nodding white flower and oval yellow fruit. Although the pulp of the ripe fruit is edible, the roots, leaves, and seeds of the plant are poisonous.
2. The fruit of this plant.

Though poisonous when green, the yellow, egg-shaped May apple can be safely eaten after ripening. This member of the barberry family is about the size of a large cherry. It's lightly sweet and acidic and makes very good preserves. The May apple is found in the East but is rarely available in markets.

The noun has 2 meanings:

Meaning #1: edible but insipid fruit of the May apple plant

Meaning #2: North American herb with poisonous root stock and edible though insipid fruit
  Synonyms: mayapple, wild mandrake, Podophyllum peltatum