ABSTRACT
The number of species within the genus Citrus is highly controversial, ranging between 16 and 157. Flowering is apparently retarded by juvenility hormones translocated from the roots at a stage when values of root/top ratios are relatively large. Juvenile citrus plants are characterized by long and strong thorns, vigorous vegetative growth with long internodes, and lack of flowers. Like most subtropical evergreen woody plants, flower induction starts during the winter and merges without interruption into differentiation, and bloom. The particularly early bloom of the trifoliate orange is probably due to the fact that flower buds are almost perfect before winter, as a consequence of its deciduous habit; the late bloom of kumquats is due to strong innate dormancy. Citrus trees produce a very large number of flowers, 30 to 150 times more than they can bear fruits. The main differences between flowers of different Citrus species concern the size and color of petals on the abaxial side of the flowers.
