Facultative Apomixis in an Endangered Dioecious Species, Woonyoungia septentrionalis (Magnoliaceae)

The breeding system of an endangered dioecious species, Woonyoungia septentrionalis (Dandy) Law, was studied in two natural populations, the Mulun population and the Dahuangni population, in Guangxi Province, China from June 2001 to early September 2002. The female flowers from previously bagged buds were treated respectively with paper bags, net bags and hand pollination by comparing with natural pollination. The results showed that female flowers treated with paper bags, net bags, hand pollination, and natural pollination all set fruits and seeds, but there was great difference in their fruit set, seed set, pre-emergent reproductive success (PERS) and seed germination rate for two populations. In both populations, PERS of hand pollination and natural pollination were higher than those of paper bagged and net bagged treatments. Among them, PERS of hand pollination was the highest, and PERS of net bagged treatment was the lowest. Both sexual reproduction and apomixis occurred simultaneously in W septentrionalis and seeds from both sexual and apomixis could germinate into seedlings. Therefore, the breeding system of W septentrionalis belonged to facultative apomixis. The apomixis in Magnoliaceae was reported for the first time.

Anatomy and ontogeny of unisexual flowers in dioecious Woonyoungia septentrionalis (Dandy) Law (Magnoliaceae)

Woonyoungia septentrionalis （Dandy） Law is aceae. The floral morphology and structure of the species a dioecious species with unisexual flowers in Magnoliare conspicuously different from other species and are important to the study of floral phylogeny in this family. The floral anatomy and ontogeny were investigated to evaluate the systematic position of W. septentrionalis, using scanning electron microscopy and light microscopy. All of the floral organs are initiated acropetally and spirally. The carpels are of conduplicated type without the differentiation of stigma and style. The degenerated stamens in the female flowers have the same structures as the normal stamens at the earlier developmental stages, but they do not undergo successive development and eventually degenerate. The male floral apex was observed to have the remnants of carpels in a few investigated samples. As the bisexual flower features could be traced both in the male and female flowers in W. septentrionalis, it suggests that the flower sex in Magnoliaceae tends toward unisexual. As well as the unisexual flowers, the reduced tepals and carpels and concrescence of carpels conform to the specialized tendency in Magnoliaceae, which confirms the derived position of W. septentrionalis in this family. As the initiation pattern of floral parts of W. septentrionalis is very similar to other species in this family, it needs further investigation and especially comparison with species in Kmeria to evaluate the separation of Woonyoungia.