St. Anthony Dunes evening primrose

Pachylophus psammophilus A. Nelson & J. F. Macbride, Bot. Gaz. 61: 32. 1916; Oenothera cespitosa Nuttall var. psammophila (A. Nelson & J. F. Macbride) Munz

Herbs perennial, caulescent, glabrous, also with resinous exudate, especially on younger leaves; from woody taproot. Stems decumbent, usually branched, 10–30 cm, becoming woody and buried in sand. Leaves (6–)8–9(–14.2) × (0.7–)1.5–2(–3.1) cm; petiole 3–9 cm; blade narrowly oblanceolate to oblanceolate, margins usually subentire or repand or remotely dentate, rarely serrate, apex acute. Flowers 1–3 per stem opening per day near sunset, with sweet scent; buds erect; floral tube 42–60 mm; sepals 22–28 mm; petals white, fading rose pink to rose, 23–40 mm; filaments 17–19 mm, anthers 13–16 mm; style 60–72(–88) mm, stigma exserted beyond anthers at anthesis. Capsules somewhat curved and often somewhat twisted, lanceoloid-cylindrical, nearly cylindrical, (20–)30–47 × 7–8 mm, gradually tapering to apex, 6–8 mm, dehiscent nearly throughout their length, valve margins with a conspicuous, irregular, wavy ridge; pedicel 1–5 mm. Seeds numerous, in 2 distinct rows per locule, narrowly obovoid, 2.5–3 × 1.2–1.4 mm, embryo 7/8 of seed volume, surface finely reticulate; seed collar with a broad membrane sealing cavity, margin entire. 2n = 14.

Flowering May–Jul. On barren areas of drifting sand at interface between outcrops of lava and sand dunes; of conservation concern; 1500–1700 m; Idaho.

Oenothera psammophila is known only from the dune area north and west of St. Anthony, Fremont County. It is unique in Oenothera because of the exu­date produced on the leaves to which sand particles adhere, forming a sand sheath, presumably for protection from the constantly blowing sand particles. It is self-incompatible (W. L. Wagner et al. 1985; Wagner 2005).