The common name of Paris quadrifolia, a poisonous woodland plant with one black berry, is herb-paris.
Paris quadrifolia is a perennial Eurasian woodland herb in the family Melanthiaceae. Its name reflects its usual four leaves, arranged in a single whorl beneath one small, star-like flower. The plant typically produces just one berry, which can look like a blueberry but is poisonous because it contains steroidal alkaloids including solanine.
The name can cause confusion because the plant is also called true lover’s knot, while “Paris” is its botanical genus rather than a reference to the French capital. Other woodland plants in the options are not equivalent names: mayapple has a different fruit and toxicity profile, black bryony is a climbing vine, and dog’s mercury is an unrelated herb.
Paris quadrifolia flowers mainly in June and July and grows in damp, shaded, often calcareous soils. Its single berry’s unpleasant taste probably helps explain why poisonings are uncommon despite its conspicuous appearance.