Onagraceae, also known as the Willowherb family or Evening Primrose family, are a family of flowering plants. The family includes about 640-650 species of herbs, shrubs, and trees in 20-24 genera. The family is widespread, on every continent from boreal to tropical regions.
The family includes a number of popular garden plants, including evening primroses (Oenothera) and fuchsias (Fuchsia). Some, particularly the willowherbs (Epilobium) are common weeds in gardens, e.g. Fireweed.
The family is characterised by flowers with usually four sepals and petals; in some genera (e.g. Fuchsia), the sepals are as brightly coloured as the petals, giving the impression of a flower with eight petals.
The seeds are very small, in some genera (e.g. Epilobium) with a tuft of down and wind-dispersed, in others (e.g. Fuchsia), in a juicy berry and dispersed by birds. The leaves are commonly opposite or whorled, but are spirally arranged in some species; in most, they are simple and lanceolate in shape. The pollen grains in many genera are loosely held together by viscin threads, meaning that only bees that are morphologically specialized to gather this pollen can effectively pollinate the flowers (it cannot be held effectively in a typical bee scopa). Accordingly, nearly all of the bees that visit onagraceous flowers are floral specialists (oligoleges).
The family is named after the genus Onagra (now known as Oenothera) in 1836 by J. Lindley in the second edition of Nat. Syst. Bot.