Why is a christmas cactus a caryophyllales?

Subcl consisting of 13 families, and about 11,000 species of angiosperms - the bulk of the subcl often referred to as the Centrospermae. The Caryophyllidae is a distinctive group usually defined by the presence of betalain pigments rather than anthocyanins, free-central (hence the name "Centrospermae") or basal placentation in a compound ovary, and an impressive list of anatomical and embryological features