The scientific classification of Old Man Cactus and Periwinkle 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. Old Man Cactus and Periwinkle kingdom and all other plants kingdom is Plantaea.
Plant family is the group of plants which have something in common. Old Man Cactus and Periwinkle family is a major factor of Old Man Cactus and Periwinkle 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. Old Man Cactus belongs to the family Cactaceae and Periwinkle belongs to the family Apocynaceae.
While comparing scientific classification, Old Man Cactus and Periwinkle genus and other classification are also important. Also, when you compare Old Man Cactus and Periwinkle, other factors should also be taken into considerations like order, subfamilies, tribe, clade etc. First plant's genus is Cephalocereus and other plant's genus is Catharanthus. Old Man Cactus tribe is Pachycereeae and Periwinkle tribe is Not Available. Old Man Cactus clade is Angiosperms, Core eudicots and Eudicots and order is Caryophyllales whereas Periwinkle clade is Not Available and order is Geraniales. Every plant have subfamilies. Old Man Cactus subfamilies are, Cactoideae and Periwinkle subfamilies are Not Available. In this way you can compare scientific classification of Old Man Cactus and Periwinkle and other products also.