R.T.Clausen (M.Peck) 1942 - Clausen RT (1942) Studies in the Crassulaceae-III. Sedum, Subgenus Gormania, Section Eugormania. Bulletin of The Torrey Botanical Club 69: 27-40. doi: 10.2307/2481519.
There is no corrections for Sedum laxum subsp. heckneri yet.