Sulphur Buckwheat (Eriogonum umbellatum) is a gorgeous mat-forming perennial with beautiful, long-lasting  yellow flowers that become tinted with red towards the end of summer. This species of Eriogonum has low growing, glossy leaves that turn burgundy through the winter, making it an excellent groundcover with all season interest! Use near the fronts of garden beds or borders, cottage gardens, rock gardens, or as a groundcover. Sulphur Buckwheat is highly tolerant of urban pollution and suitable for city sites. 
Photo Credit: C T Johannson