Fourpoint Evening Primrose (Oenothera rhombipetala): yellow Minnesota wildflowers

Fourpoint Evening Primrose

Plant Info
Also known as:	Rhombic Evening Primrose
Scientific name:	Oenothera rhombipetala
Family:	Evening Primrose (Onagraceae)
Life cycle:	annual or biennial
Origin:	native
Habitat:	sun; dry prairies, along roads
Bloom season:	summer
Plant height:	1 to 3 feet
USDA PLANTS database:	Minnesota county distribution map

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Flower:: Flowers are whorled around the stem at the top of the plant in a spike up to 12 inches long, blooming from the bottom of the spike up. Individual flowers are 1 to 2 inches across with 4 diamond-shaped petals and 8 long yellow stamen. The flowers bloom at night and close up in the morning. One plant may have several spikes, each at the end of branching stems.
Leaves:: Leaves are narrow and twisted with wavy edges, to 4 inches long and ¾ inch wide, with little or no leaf stem. Attachment is alternate and the leaves are often crowded on the stem. First year plants have a basal rosette of stemmed leaves that are broadest at the tip end.
Notes:: Fourpoint Evening Primrose is on the Special Concern list for Minnesota. At Wild River State Park they've made a serious effort to repopulate the prairie areas with this plant and it seems to be doing quite well.

Photos taken at Wild River State Park, Center City, MN July 2007 and June-July 2008

Have you seen this plant in Ramsey County, or have any other comments about it?