General: Longstem Evening Primrose (Oenothera longissima) is an upright, biennial forb that opens large, yellow flowers in the evenings of its second year. The plant grows to 6-ft tall, which is much taller than most of our Evening Primroses. The stem is stout and often reddish. The leaves are several inches long, narrow, and with entire or dentate (outward pointing points) margins. The yellow flowers are large, with petals spreading to 3-4 inches across, and age to orange or red. The hypanthium (the tubular stalk behind the petals) is very long (60- to 135-mm).

Longstem Evening Primrose is superficially similar to Tall Evening Primrose, but in the later species, the hypanthium is much shorter (20- to 50-mm).

Longstem Evening Primrose is an uncommon component of vegetation communities in moist meadows and woodlands from sea level to 5,000 ft elevation in the Upper Sonoran (Mojave Desert Scrub and Pinyon-Juniper Woodland) life zone. Around Las Vegas, look for Longstem Evening Primrose around springs in Red Rock Canyon NCA and Desert NWR.

Family: Evening Primrose (Onagraceae)