Environmental Control of Flowering of Boronia megastigma (Rutaceae) and Hypocalymma angustifolium (Myrtaceae)

Abstract

The flowering responses of Boronia megastigma Nees (Rutacae) and Hypocalymma angustifolium Endl. (Myrtaceae) to different photoperiod and temperature regimes were similar despite the fact that these species are from different families. No flowers reached anthesis in a temperature regime of 25°C day/17°C night but flowering of both species occurred in a cool temperatures (17°C day/9°C night). Photoperiod had no effect on flowering at the temperatures tested. Ten weeks of cool temperatures (17°C day/9°C night) were required for a maximum number of flowers to reach anthesis on H. angustifolium plants whereas B. megastigma plants required 15 weeks. Flower development in both species was inhibited by a large difference between day and night temperature (21°C day/5°C night) and promoted if the day/night difference was reversed (9°C day/17°C night). The temperature of the aerial parts of the plant controlled flowering, whereas vegetative growth was controlled by root temperature. Therefore, while a reduction in vegetative growth naturally coincides with the production of flowers, these events are not necessarily linked.