A pilot study of the breeding system of Henry’s St John’s wort, Hypericum pseudohenryi

A pilot study of the breeding system of Henry’s St John’s wort, Hypericum pseudohenryi
Carryn Smith1,2, Ingrid Nänni 2
1University of KwaZulu-Natal; 2Invasive Species Programme, SANBI

Henry’s St John’s Wort (Hypericum pseudohenryi) is an invasive alien plant found in the KwaZulu- Natal Drakensberg and Midlands that has been perceived as a threat. Once established, this species can invade watercourses and undisturbed veld. As it is widely established, it was expected that the plant is able to self-pollinate with a large degree of success. To test whether this is true, pollinator exclusion experiments were conducted at three study sites in the Drakensberg and Midlands. Further pollination tests were done to establish the role of local pollinators. There were three different treatments: emasculated flowers, hand pollinated cross- pollination, and bagged flowers to exclude pollinators and encourage self-pollination. The results show that while plants are able to undergo self- pollination  and  produce  seeds,  the  number  of  seeds  produced  through  self-pollination  was significantly lower than the control samples, which were chosen at random on the plant. However, self-pollinated seed set did not differ significantly from flowers where the anthers were removed. There was no significant difference in seed set between control flowers and hand-pollinated flowers. This shows that while the plant is self-compatible, pollinators are still required to increase seed set through cross pollination. The low number of seeds in the flowers where the anthers were removed is possibly due to pollinators being attracted by pollen as a reward, thus not visiting emasculated flowers. Further testing will be done to determine whether these results are true across the whole flowering season.