YELLOW SUNDROPS Oenothera serrulata (Syn. Calylophus serrulatus) (Yellow Sundrops, Plains yellow primrose) is a plant without a lot of press, but it is amazingly beautiful.  Pictured in the lower right in the photo at the left. It blooms with Poppymallow, butterfly milkweed, pale coneflower and prairie phlox.  In the prairie, it is a diminutive plant, but in a landscape …