Name and distribution
Kew accepts Lophophora diffusa (Croizat) Bravo and gives its range as Querétaro to Hidalgo, Mexico. Its treatment includes koehresii in synonymy.
Read the body as well as the flower
The Flora of North America notes yellow-green stems in L. diffusa within its genus description. Color is one descriptive character; photographs under different light should not be used as a stand-alone species test. Keep the stem, areoles, flowers and original source record together.
Historical anatomy is not a modern family tree
Older authors’ interpretations of simple pollen or body structures are historical hypotheses. They do not establish that a living species is the ancestor of the others. See the genus overview.
Keep source distinctions
Retain any koehresii or other population label exactly as acquired and record the supplier. Changing the accepted species field should not erase a documented source distinction.