Cream Cups

Cream Cups © KKorbholz

Platystemon californicus

Description (Jepson,

  • Eudicotyledon
    • Eudicots are a major lineage of flowering plants; see family for general characteristics
  • Poppy Family (Papaveraceae)
    • Only species in this genus
  • Annual herb
    • Shaggy hairy
  • Leaves
    • Basal are alternate (1 leaf at each junction with stem)
    • Cauline (along the stem) are whorled (3 or more leaves/flowers at each junction with stem)
    • Linear and hairy, with rounded or pointed tips
  • Flowers
    • Inflorescence (flower arrangement) is of solitary flowers, with nodding buds
    • 6 ovate, white to cream petals, sometimes with a yellow base
    • Many stamens, with broad filaments
    • 3 hairy sepals (usually green, outer flower parts)
      • Sepals drop off when flower opens
    • Ovary superior (attached above other flower parts)
  • Fruit is a unique schizocarp (see Notes)
  • Height to 12 in.
Fruit © DSchiel


  • Native to California
    • Grows in grasslands
    • 55-64% of plants occur on ultramafic soils, e.g. serpentine; see ultramafic affinity rankings (Calfora per Safford and Miller 2020)
    • See Serpentine Grassland for more about Edgewood’s serpentine soil and the unique communities it supports
    • See Calflora for statewide observations of this plant
  • Outside California, grows in Oregon, Utah, Arizona, and into Baja California, Mexico
  • Grows at elevations to 3,280 ft.

Uses (San Mateo County Parks prohibits removal of any natural material)

  • Wildlife
    • Frequented by insects, mainly for pollen, e.g. solitary bees (Andrenidae and Halictidae)
    • Larval food source (host) for fairy some long-horn moths, e.g. Opler’s longhorn moth (Adela oplerella)
  • Native people
    • Leaves were eaten

Name Derivation

  • Platystemon (pla-tee-STEM-on) – from the Greek platus, “broad,” and stemon, “stamens,” referring to the flattened stalks of the stamens


  • Primarily wind pollinated (Hannon 1981)
  • Highly variable in appearance
  • Flowers open in the morning and close in the evening or when it’s cloudy
    • 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)
  • Has a fruit unique to the plant world (Prigge 2013)
    • While still attached to the plant, the fruit breaks apart lengthwise into strips
    • After detaching from the plant, the strips break into single seeds
    • This unique fruit has been compared to “tiny ears of corn with the husks removed” (Lady Bird 2021)

ID Tips

  • Unlikely to be confused with any other plant in Edgewood’s grasslands

At Edgewood

  • Found in serpentine and non-serpentine grasslands
  • Flowers March – April

See General References

Specific References

Alexander, E.B. 2010, Oct. and 2011, Jan. Serpentine soils and why they limit plant survival and growth. Fremontia 38/39: 28-31.

Hannan, G. 1981. Flower color polymorphism and pollination biology of Platystemon californicus Benth. (Papaveraceae). American Journal of Botany 68: 233-243. JSTOR.

Lady Bird Johnson Wildflower Center. 2021. Playtystemon californicus. Plant Database. University of Texas at Austin.

Prigge, B.A. and A.C. Gibson. 2013. Platystemon californicus. A Naturalist’s Flora of the Santa Monica Mountains and Simi Hills, California. Web version, hosted at Wildflowers of the Santa Monica Mountains National Recreation Area. United States Department of Interior, National Park Service.

Safford, H.D. and J.E.D. Miller. 2020. An updated database of serpentine endemism in the California flora. Madroño 67(2): 85-104. BioOne Complete. PDF hosted by San Diego State University, San Diego, California.

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.