Erysimum pulchellum - Mustard Wallflower
This alpine evergreen perennial comes to us from Turkey, Armenia, and Iran. The plant forms a low, dense mat only 2 inches high, but spreading to 2 ft wide. A very dense groundcover. The flowers come out in late March and are a bright sunny mustard yellow color, and last until mid April. Excellent when allowed to cascade over a wall or down the face of a rock. Not widely known or available. A favorite among rock gardeners. Hardy to zone 6.