Meadow sundrops, Oenothera pilosella
 
A short evening primrose with showy flowers for the front of a border. Meadow sundrops grow to only 30 to 60 cm in height. Their large, cheery yellow flowers bloom in June and July and open during the day, as opposed to evening primrose, which flowers open in the evening. This perennial plant is easy to grow and can spread quickly by rhizomes, filling in empty spaces and forming great ground-covering mats. It could be considered the most cheerful groundcover. Its shallow root system makes it easy to keep at bay.
 
Ecology:
Meadow sundrops attract many pollinators, including Toronto's official bee, the metallic green sweat bee. Birds, such as dark-eyed juncos, love the seeds. Meadow sundrops are the host plant for the beautiful pink primrose moth and many other moth species. It also provides pollen to pollen specialist bees. 
 
Growing conditions:
In the wild, sundrops occur in prairies, old fields, wet uplands, wet grassy areas, and along roads and railroads. In the garden, sundrops prefer medium to wet clay soil and full sun. However, they can grow in any soil type, including poor soils and light shade. They are drought-tolerant once established and somewhat salt-tolerant, which makes them great boulevard plants.