This plant was added as Agave leopoldii in April 2015. When I updated the Agave entries earlier this month, I learned that A. leopoldii is classified as a synonym for A. parryi, so I made the correction in the entry.
It's true that this plant is listed all over the Internet as Agave x leopoldii, but this hybrid taxon is not an accepted botanical name because it is a man-made hybrid rather than a spontaneous one that occurred in the wild.
I've now corrected the entry by removing the species name. The plant is now listed as a hybrid agave. Any other "x leopoldii" plants in our database can be corrected in the same way, either by moving them to the generic entry if there is no cultivar name or by deleting the species name if there is a cultivar name.