In higher plants, individuals are classified as males, females or hermaphrodites, on the basis of whether the flower possesses only anthers, or only ovary or both. It is believed that the primitive type of floral condition in these plants was hermaphroditism, where flowers are bisexual. A range of types from these hermaphrodites to those having unisexual flowers with no trace of other sex are known in higher plants. These variations in higher plants are listed in Table 17.5. Of the eight types listed in Table 17.5, we have relatively better information on dioecious plant species and mechanism of sex determination in only these dioecious plant species will be discussed in this section.
(1940) gave a list of plant species in which sex chromosomes had been reported. Subsequently Wastergaard (1950) prepared a list of plant species where the presence of a pair of heteromorphic sex chromosomes was well established and also of those where it was not so well established. For some dioecious plant species, the different types of chromosome constitutions involving heteromorphic sex chromosomes in one sex are listed in Table 17.6.