Ruby E. Stephens, PhD Candidate at Macquarie University
Everyone loves flowers. They look good, they smell good, and if you pick the right flowers (pineapple sage, anyone?) they even taste good. Flowers play symbolic roles in all sorts of human rituals: rose bouquets at weddings, white lilies at funerals, bright orange marigolds at Mexican or Hindu festivals.
Flowers are so symbolised in our culture that we often forget the ecological, biological roles flowers play. Flowers are very important to the plants that bear them. For most plants, flowers attract pollinators to make seeds, helping plants to reproduce and form the next generation. Flowers also play important roles in ecosystems. Floral nectar, pollen and even petals are an important food source for a huge range of animals, from bees and beetles to birds and bats. In Australia nectar from our main tree genus, Eucalyptus, is a hugely important food source. Migratory birds like the Swift Parrot (Lathamus discolor) and bats like the Little Red Flying Fox (Pteropus scapulatus) often move with eucalypt flowering across the landscape.
Despite the importance of flowers to ecosystems flowers and floral traits have rarely been studied at a large, landscape scale. This is where my PhD comes in – I’m trying to use floral traits, such as flower size, flowering time, or even a flower’s pollination syndrome, to explore some of the large-scale patterns in how flowers vary, across Australia and the world.
Measuring floral traits can be a lot trickier than measuring, for example, leaf traits. Flowers aren’t always there to measure, to start with. This timing of what plants flower when is itself a floral trait though. Flowering time can tell us a lot about the relationship of flowers with climate, and what floral resources are available when. My first PhD paper combined plant survey and trait data to map the flowering time of plant communities across Australia, and showed that flowering windows are shorter and more concentrated in parts of Australia where temperature is low, rainfall is high, and the climate is more predictable. Across much of Australia though rainfall is low and the climate is unpredictable, and plants in such environments flower at any time of year in response to conditions (read more here).
Floral traits can also be tricky to measure because of the incredible diversity of forms that flowers have evolved. This diversity makes flowers difficult to measure consistently across species. ‘Regular’ flowers have four parts – sepals, petals, stamens and the pistil. Many flowers are irregular though, with different parts fused together, shrunken, enlarged or curiously arranged to create the huge and sometimes overwhelming diversity of flowers that fill our world.
All these features have evolved to maximise the chance a flower will be pollinated, whether by animals like insects or birds or abiotically by wind or water. My latest PhD chapter classifies flowers as wind, water, insect or vertebrate pollinated to map the evolution of pollination across the flowering plants. I used an evolutionary tree for the flowering plants to sample species in every flowering plant family. My models show that the ancestral flower was very likely insect pollinated, and wind and vertebrate pollination have evolved numerous times from that insect pollinated ancestor (read more here).
This really drives home to me how important ecological interactions are: flowers have evolved in response to insect pollination for hundreds of millions of years. If you find a flower beautiful today, you most likely have insects to thank for it.
