Napa cabbage might have originated from natural hybridization between turnip (Brassica rapa subsp. "Brassica rapa" species are diploid and have 10 chromosomes. Bok choy (American English), pak choi (British English), or pok choi ("Brassica rapa" subsp. It is a pest of "Brassica oleracea", "Brassica rapa" and "Brassica napus". Since the turnip had been named first by Linnaeus, the name "Brassica rapa" was adopted. The plant specimen studied in the PGF was Brassica rapa (turnip). The term "turnip" is also used for the white turnip ("Brassica rapa" ssp "rapa"). Yellowed plants of Chinese cabbage and pak-choi ("Brassica rapa") can be infected by "S. citri".