Breeding systems in Gingidia dawson and related genera of the umbelliferae.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Field observations of sex conditions were made and flowering and fruiting material collected from populations of all species of Gingidia, Scandia and Lignocarpa s.l., and representative species of Anisotome and Aciphylla. Sex ratios show a predominance of males in populations of both gynodioecious and dioecious species. This is postulated, in dioecious species, to be the result of males flowering more frequently and surviving longer than females. In gynodioecious species there is a relationship between the sex ratio and the relative ovule contribution. Inbreeding effects in the progeny of males are postulated to account for a discrepancy between the theoretical and experimental results for this relationship. The breeding systems are described in functional as well as morphological terms. Pollen function is almost entirely confined to male plants. Ovule function, as assessed by fruit number and quality, is concentrated on female plants, but males of gynodioecious species function via ovules to various degrees. The sexual performance of both male and female plants is consistent over several flowering years, both in the sex of plants and in the extent to which male plants contribute via ovules. The flowering periods of male and female plants were studied in detail. Males and females begin flowering simultaneously, but females reach their flowering peak more quickly and finish flowering earlier than males. This is considered to be an adaptation promoting pollination of the ovules of females while allowing time for fruit to mature. There is a wide range of fruit sets between male plants of a population. A range of average male fruit set form 0 to 80% is found between populations. Different populations also show a range from 0 to 50% female plants. This is considered to be evidence for the evolution of dioecy from hermaphroditism via gynodioecy. The description of breeding systems in these genera shows that gynodioecy is best considered as a range of breeding systems rather than as a single system.