ABSTRACT
According to the Engler system the plant kingdom has thirteen divisions; the thirteenth (Embryophyta Siphonogama) corresponds to the Spermathophyta. Lower taxonomic ranks are the following:
Subdivision: Angiospermae Class: Monocotyledoneae
Order: Geraniales Family: Rutaceae
Subfamily: Aurantioideae
Although other subfamilies exist within the Rutaceae, all citrus belong to the Aurantioideae subfamily, that includes two tribes: the Clauseneae, that are the very remote and remote citroid fruit trees, with five genera, and the Citreae, that are the citrus and citroid fruit trees, with three subtribes that are the Triphasiinae or minor citroid fruit trees (eight genera), the Balsamocitrinae or hard-shelled citroid fruit trees (seven genera) and the Citrinae or citrus fruit trees (thirteen genera) where the so called true citrus genera i.e. Citrus, Poncirus and Fortunella are included (Swingle and Reece, 1967).
