In my travels around West Texas, I drove by these plants 2 or three times before I took the time to stop and see them up close. It was either too dark, or I was not with camera, or I had others in the car and couldn’t stop. When I finally made it to the location, I was more than glad I did.
Diamond Petal Primroses are a biennial plant which means that it takes two years of growth and development before they flower. Most primroses that I have encountered in Texas grow low to the ground and spread out to cover large spaces with their leaves and ultimately flowers. Diamond Petal Primroses, Oenothera rhombipetala, grow straight up for 2 to 3 feet before they produce a spike of flowers. You can find these flowers in the plains states as far north as North Dakota, east as far as Minnesota, and west as far as New Mexico. They like grasslands, savannahs, and woodland edges. Sandy or sandy loam soils allow its deep taproot to help them find enough water to bloom May through September. These plants tolerate dry but will bloom more if they get enough rainfall.
The 2-3 inch diameter flowers have 4 petals that come to a blunt point, rhombipetala is latin for the shape of the petals. Most primroses I have seen tend to produce round looking cup or bell shaped flowers because the petals are large and overlap. A remarkable wildflower, and it’s a shame that you only get to see them every two years.