Paris quadrifolia (Herb Paris, True lover's Knot) is a species of the genus Paris in the family Melanthiaceae, although authorities formerly regarded it as part of the Liliaceae family. It is related to Trillium, with which it can be confused. Trillium, however, is generally 3-merous (3 leaves per whorl, 3 petals etc.), whereas Paris is 4-merous.
Paris quadrifolia has solitary flowers with four or more very narrow greenish filiform (threadlike) petals and green petaloid sepals. The flower is borne above a single whorl of four or more stem leaves. It prefers calcareous soils and lives in damp and shady places, especially old established woods and streamsides. It occurs locally in temperate and cool areas throughout Europe and Asia but is absent in the wild from the Americas, Africa and the southern hemisphere. In Britain it is more frequently found in the east of the country, but it is uncommon throughout its range. Each plant only produces one blueberry-like fruit, which is poisonous.