Oenothera pilosella ssp. sessilis

Common Names:
Prairie Evening Primrose
(Pennell) Straley
Growth Habit:
CPC Number:
Profile Contributors:
Matthew Albrecht
Fully Sponsored

Reference Links

ITIS - Tropicos - USDA Plants - Fish & WildLife

Participating Institutions

The following Participating Institutions are custodians for this species in the CPC National Collection:
Missouri Botanical Garden

The conservation of Oenothera pilosella ssp. sessilis is fully sponsored.
Matthew Albrecht contributed to this Plant Profile.


Oenothera pilosella subsp. sessilis is beautiful native perennial herb with showy yellow flowers that bloom between May-June. Restricted primarily to remnant tallgrass prairies in the lower Mississippi River Valley, this species has declined dramatically in the wild due to conversion of prairie habitat to cropland and inappropriate management practices. Oenothera pilosella subsp. sessilis is one of two octoploid subspecies of Oenothera pilosella. According to Straley (1977), Oenothera pilosella subsp. sessilis can be distinguished from Oenothera pilosella subsp. pilosella in being nonrhizomatous, by narrower leaves, sessile capsules, and densely appressed hairs pubescence throughout the entire plant.

According to Tucker (1983), the following characteristics help distinguish Oenothera pilosella ssp. sessilis from Oenothera pilosella subsp. pilosella:

Pubescence of erect hairs 1-2 mm long throughout (rarely glabrous); mature ovary 9-12 mm long; sepal tips divergent. (O. pilosellas subsp. pilosella)

Pubescence of densely appressed hairs less than 1 mm long throughout; mature ovary 4.5-6.5 mm long; sepal tips connivent. (O. pilosella subsp. sessilis)

New research based on molecular, morphological, and breeding system analyses indicate that O. pilosella subsp. sessilis is clearly distinct from Oenothera pilosella subsp. pilosella and merits recognition as a species (Wagner, Hoch, and Krakos, personal communication, September 2010).

Distribution & Occurrence


Conservation, Ecology & Research