The scientific classification of Bok Choy and Cereus includes the entire classification chart that includes kingdom, family, clade, tribe etc. A kingdom is the second highest taxonomic rank. A taxonomic rank is the level that a living organisms are placed in hierarchical level of arrangement of life forms. All the living organisms are divided into kingdoms. Plant kingdom is a main classification of living organisms that include all plants. There are six kingdoms which are: Plantae, Animalia, Fungi, Protista, Aschaea/Archaeabacteria and Bacteria Eubacteria. Bok Choy and Cereus kingdom and all other plants kingdom is Plantaea.
Plant family is the group of plants which have something in common. Bok Choy and Cereus family is a major factor of Bok Choy and Cereus Scientific Classification. Plant family helps you narrow the search of your plants. It also gives you idea about, how the plant looks, how the seed will be like etc. These two plant families can be different or same. Bok Choy belongs to the family Brassicaceae and Cereus belongs to the family Cactaceae.
While comparing scientific classification, Bok Choy and Cereus genus and other classification are also important. Also, when you compare Bok Choy and Cereus, other factors should also be taken into considerations like order, subfamilies, tribe, clade etc. First plant's genus is Brassica and other plant's genus is Selenicereus. Bok Choy tribe is Not Available and Cereus tribe is Hylocereeae. Bok Choy clade is Angiosperms, Eudicots and Rosids and order is Brassicales whereas Cereus clade is Angiosperms, Core eudicots and Eudicots and order is Caryophyllales. Every plant have subfamilies. Bok Choy subfamilies are, Not Applicable and Cereus subfamilies are Cactoideae. In this way you can compare scientific classification of Bok Choy and Cereus and other products also.