E. angulosum and E. gracillimum are very similar looking. They're separated by tepals dimorphic vs. monomorphic, respectively, in the keys of both the Jepson eFlora and the FNA.

Unfortunately, the perianths aren't fully open in my photo here...so it's not clear whether the tepals are dimorphic or monomorphic. But note that the stamens (or their filaments, in the cases the anthers have dropped) are clearly exerted here...which is a character that be be used to separate E. angulosum from E. gracillimum, since the latter has stamens included.