How many cacti are in the US?

It's difficult to estimate how many cactus plants are in the United States of America. A census needs to include their native habitats, which tend to be in the southwest. But that census needs to factor in the non native habitats into which cactus plants are able to expand due to their high adaptability. It also needs to consider all of the florists, gardeners, nurseries, parks, plant sections and stores, and public gardens where cactus plants are being grown.