Here's the scientific classification of cacti, starting with the broadest category and narrowing down:

* Domain: Eukarya (organisms with cells containing a nucleus)

* Kingdom: Plantae (plants)

* Phylum: Magnoliophyta (flowering plants)

* Class: Magnoliopsida (dicotyledons)

* Order: Caryophyllales

* Family: Cactaceae (cactus family)

Note: Within the Cactaceae family, there are many different genera and species of cacti, each with its own unique characteristics.