Domain:  Eukarya

        Kingdom: Plantae

                 Phylum: Magnoliophyta

                              Class:  Magnoliopsida

                                            Order: Sapindales

                                                       Family: Rutaceae

                                                                    Genus: Citrus


                                                                        Species:  Citrus Sinensis

Citrus sinensis belongs to the domain Eukarya because it is a eukaryotic organism, meaning that the cells have a true nucleus, possess membrane-bond organelles, and the genetic material is DNA.

Citrus sinensis belongs to the kingdom Plantae because it is multicellular, has cell walls made of cellulose, and participates in photosynthesis via chloroplasts. Another organism that is classified in the Plantae kingdom is the Sweet Violet (Viola ordata)

Citrus sinensis belongs to the phylum Magnoliophyta (Angiosperms) because it is a flowering plant that uses a fruit body to protect its seeds.

Citrus sinensis belongs to the class Magnoliopsida because it shows characteristics of being a Dicotyledon such as secondary growth, non-parallel veins, and the presence of two cotyledons in their seeds.

Citrus sinensis belongs to the order Sapindales because it is a woody tree and this order consists of woody trees and shrubs.

Citrus sinensis belongs to the family Rutaceae, because these plants are often characterized as trees and shrubs, usually having strong scents.

Citrus sinensis is placed in the Citrus genus because the organisms in this family are generally edible and are a good source of vitamin C.

The phylogenetic tree to the left is a representation of the of the most basic way to separate organisms into some of the largest possible groups.    The differentiation follows C. sinensis the ancestor of all organisms to classifying it as a land plant.  From the top, all organisms are separated into three domain which are represented in blue.  Then the orange represents the five supergroups of organisms.  Lastly, green represents the separations of the supergroup Archaeplastida.  Cholrophytes and Charophyceans are classified as green algae and it as believed that it was green algae that land plants originated from.
This phylogenetic tree is a continuation of the one above and it shows some of the characteristics that land plants developed that help differentiate different species from each other.  Citrus sinensis follows the left side of the tree because it has developed vascular tissues, and seeds that have a covering.  The orange is classified as a eudicot, therefore some of the organisms that are most closely related to the sweet orange are monocots, magnoliids, and basal angiosperms.