The scientific classification of Oleander and Old Man Cactus 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. Oleander and Old Man Cactus kingdom and all other plants kingdom is Plantaea.
Plant family is the group of plants which have something in common. Oleander and Old Man Cactus family is a major factor of Oleander and Old Man Cactus 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. Oleander belongs to the family Apocynaceae and Old Man Cactus belongs to the family Cactaceae.
While comparing scientific classification, Oleander and Old Man Cactus genus and other classification are also important. Also, when you compare Oleander and Old Man Cactus, other factors should also be taken into considerations like order, subfamilies, tribe, clade etc. First plant's genus is Nerium and other plant's genus is Cephalocereus. Oleander tribe is Wrightieae and Old Man Cactus tribe is Pachycereeae. Oleander clade is Angiosperms, Asterids and Eudicots and order is Gentianales whereas Old Man Cactus clade is Angiosperms, Core eudicots and Eudicots and order is Caryophyllales. Every plant have subfamilies. Oleander subfamilies are, Apocynoideae and Hippocastanoideae and Old Man Cactus subfamilies are Cactoideae. In this way you can compare scientific classification of Oleander and Old Man Cactus and other products also.