Yellow Desert Evening Primrose

On a recent trip (early April) to El Pinacate and Gran Desierto de Altar Biosphere Reserve in Sonora, Mexico, between Sonoyta and Puerto Penasco, I encountered the yellow desert evening primrose (oenothera primiveras) right near the entrance. It is found in the southwestern U.S. (CA, AZ, NV, UT, NM and TX) and northern Mexico in desert flats below 4,500 feet. It has a rosette of green or grayish leaves that are cut into deep lobes or teeth and wavy or crinkled edges. 

Yellow desert evening primrose

The flower can bloom from February to May and has four heart-shaped yellow petals which will fade to orange or red as they age.