Just a few days ago, as I hiked Gregory Canyon west of Boulder, I saw the common sulphur flower in its full glory. This is Eriogonum umbellatum v. umbellatum, the type form of the most universal of western buckwheats. There are those who don't like yellow in the garden: to them, I say "fiddlesticks" or "phooey!". Nature loves yellow, and lavishes it everywhere...There are dozens of subspecies of just this one species of buckwheat: I've grown nearly a dozen in my day. But these two forms are the ones that have stuck by me longest.
Here a month ago is the Western slope subspecies of E. umbellatum, var. aureum, in Wildflower Treasures garden.