U. S. Fish and Wildlife Service Photo CLICK PHOTO FOR A LARGER IMAGE

Oenothera psammophila Nels. & Macbr.

St. Anthony evening-primrose; St. Anthony sand-lily

Onagraceae (Evening-primrose family)

Synonyms: Oenothera caespitosa Nutt. var. psammophila (Nels. & Macbr.) Munz

General Description: A glabrous, herbaceous perennial from a thick taproot 10-30 cm tall. Stems can become woody and buried in the drifting sand and give rise to numerous branches that then emerge from the sand. The multiple stems and branches can give plants a clumped or bunchy appearance spreading up to about 60 cm wide. Leaves are usually 7-15 cm long and 1-3 cm wide, reverse lance-shaped, and entire or with wavy teeth along the margins. Flowers are borne singly in the leaf axils. Petals are bi-lobed at the summit, 2.5-4.5 cm long, and white, but turn pink or reddish-purple with age. The sepals are reflexed and 2-3 cm long, while the floral tube is 4-6 cm long. The sessile, ascending or erect fruit capsules are cylindric in outline, strongly angled, 3-5 cm long, and become rather woody at maturity, with the open capsules sometimes remaining attached to the stem throughout the winter.

Photo © Robert K. Moseley CLICK PHOTO FOR A LARGER IMAGE

Illustration.

Field Identification Tips: St. Anthony evening-primrose is recognized by its clumped, hairless habit, large white flowers that fade pinkish to reddish, and sessile capsules twisted and curved near the top that lack distinctive rows of warty projections. The distinctive sandy, inter-dunal habitat is also a good tip.

Phenology: Flowers June and July.

Similar Species: St. Anthony evening-primrose is most likely to be confused with one of the varieties of Oenothera caespitosa (evening-primrose) that occur in the St. Anthony area. Oenothera caespitosa var. marginata has straight capsules on short pedicels with distinctive wart-like projections in ridges or rows. In addition, plants are usually obviously hairy, with more deeply toothed leaves, and floral tubes usually over 7 cm long. Oenothera caespitosa var. caespitosa is often (but not always) shortly pubescent to one degree or another, and has leaves all in a basal cluster. It also has fruit capsules that are not twisted and only slightly curved at the top. Oenothera pallida (pale evening-primrose) is a rhizomatous perennial that sometimes co-occurs with St. Anthony evening-primrose. It generally has a more erect habit, poorly developed or no basal leaves, usually smaller flowers, and more or less spreading, sometimes rather contorted fruit capsules.

Idaho Conservation Data Center Photo CLICK PHOTO FOR A LARGER IMAGE

Habitat: The trailing margins of migrating sand dunes in inter-dunal areas having sand-filled cracks over basalt outcrops and developing primary plant communities. St. Anthony evening-primrose is apparently limited to areas where the sand is less than approximately 50 cm deep. Associated species include Leymus flavescens, Achnatherum hymenoides, Psoralea lanceolata, Ipomopsis congesta, Oenothera pallida, and Lygodesmia juncea. Plants do not occur on the bodies of sand dunes, nor in surrounding sagebrush-steppe habitats.

Global Distribution: Endemic to the St. Anthony Sand Dune complex in eastern Idaho.

Idaho Distribution: The St. Anthony Sand Dune complex in southwestern Fremont County.

References:

Cronquist, A., N. H. Holmgren, and P. Holmgren. 1997. Intermountain Flora. Vascular plants of the Intermountain West, U.S.A. Vol. 3, Part A. The New York Botanical Garden, Bronx, NY. 446 pp.

Lee, V. R. 1983. Oenothera psammophila (Nels. & Macbr.) Wagner, Stockhouse & Klein ined. in the Fremont County, Idaho sand dune system. Unpublished M.S. thesis. University of Idaho, Moscow. 151 pp.