Evening Primrose Family

Farewell-to-Spring © TCorelli

Onagraceae (on-uh-GRAY-see-ee)

Iconic Features

  • Flower parts in fours
  • Inferior ovary
  • Often open at dawn or dusk

Description (Jepson)

  • Eudicotyledons (eudicots) – a major lineage of flowering plants including most plants traditionally described as dicots and generally characterized by
    • 2 seed leaves (dicotyledon)
    • Netted (reticulate) leaf venation
    • Flower parts in fours and fives
    • Pollen grains with 3 pores (tricolpate)
    • Vascular bundles in stem arranged in a ring
    • Taproot system
  • Annuals or herbaceous perennials
  • Leaves
    • Generally simple (not divided into leaflets) and toothed
    • Alternate (1 leaf at each junction with stem), opposite (2 leaves at each junction with stem), or whorled (3 or more leaves at each junction with stem)
  • Flowers
    • Usually bisexual and radially symmetric
    • In parts of 4, with 4 petals and 4 sepals (usually green, outer flower parts)
      • Sepals generally fold back (reflex)
  • Pollen has cobweb-like (viscin) threads
    • Bees in general have specialized electrostatic hairs called scopa (plural, scopae) that store pollen while foraging (Kerstiens 2019)
    • Many bees who visit plants in the Evening-primrose family have evolved modified hairs to handle the sticky pollen characteristic of this family (Portman 2017) 
    • Pollen with viscin threads has been found in only two other, unrelated plant families: in some members of the Heath family (Ericaceae), including Rhododendron, and of the Pea family (Fabaceae) (Sarwar 2007)
      • This is an example of convergent evolution
  • Sepals, petals, and stamens (male flower parts) fused at base into a cup-like structure (hypanthium)
    • Sometimes lengthened into a floral tube
  • Ovary inferior (below the attachment of other flower parts)
  • Often open at dawn or dusk
    • This process is an example of nyctinasty, which refers to diurnal and nocturnal changes (single or repetitive) exhibited by the leaves and flowers of some plants (van Doorn and van Meeteren 2003)
  • Fruit usually a capsule (dry, multi-chambered pod that splits open) with many small seeds


  • Approximately 657 species worldwide, in a wide range of habitats
    • Found in California from coastal dunes to alpine regions and in deserts and wetlands
    • Includes clarkias, suncups, willowherbs, and fuschias
  • Scientific name from the genus Onagra (now Oenothera), from the Greek for “(food of) the ass”
  • Distinct from the similarly-named Primrose family (Primulaceae), which includes the common ornamental primrose and shooting stars
  • Represented by 11 species at Edgewood

See General References

Specific References

Kerstiens, H. 2019, Apr. 3. Charged electrostatic hairs collect pollen granules. Ask Nature. Biomimicry Institute.

Portman, Z. 2017, Jul. 6. The stickiness of Onagraceae pollen. The Science of Species: Understanding and Identifying the Bees of North America.

Sarwar, A.K.M. 2007, Mar. Pollen Morphology and Its Systematic Significance in the Ericaceae. Dissertation. Graduate School of Agriculture, Hokkaido University, Sapporo, Japan. Pg. 225.

van Doorn, W.G. and U. van Meeteren. 2003, Aug. 1. Flower opening and closure: A review. Journal of Experimental Botany 54: 1801–1812. Oxford Academic.

Browse Some Edgewood Plants in this Family