I bought a Lophophora williamsii plant online also called peyote and it was sold to me as L. Williamsii var. Texensis which would be the Texan/northern variety of LW. So in my research to know if mine was LW or L Diffusa I learned some helpful information. Here's the nutshell version LW. Straight deep rib furrows and green blueish/gray color with 5 to 8 ribs usually and no more than 13 I believe. Pink flowers with darker pink stripe down the center of the petals. L Diffusa_ Green with yellowish tone more rounded with shallow rib furrows and they're wavy. White flowers. Hopefully someone else can pick up where this leaves off and correct any errors if necessary.
