Plants that have flowers that point towards the sky may be better at attracting pollinators than plants that have ‘shy’ flowers that point sideways. The study, by researchers in the USA, Germany and South Africa, used two species – Zaluzianskya natalensis and Zaluzianskya microsiphon – to investigate the idea that flower orientation, in combination with floral scent, affects the behaviour of pollinators.
Both flowers are open in the evening, and attract hawkmoths, which pollinate them. In the experiment, hawkmoths showed a preference for Z. natalensis flowers. Z. natalensis produces more floral volatiles than Z. microsiphon – it has a stronger scent to pollinators – but artificially adding more volatiles to the flowers had no effect on the numbers of hawkmoths that visited.
The secret of Z. natalensis’ success doesn’t appear to be its smell. Z. natalensis, however, also has flowers that point upwards. The researchers found that manipulating the flowers of Z. microsiphon to point upwards increased their appeal to hawkmoths, and that manipulating the flowers of Z. natalensis reduced their appeal.
This study, published in New Phytologist, shows the importance of flower orientation in affecting how pollinators behave, which in turn influences the reproductive isolation – the chance of inter-breeding – that those plants experience.