August flowers and their visitors

 Another week, another reminder that nature isn’t as simple as we think. I was going to write about pollination syndromes, suites of flower traits that supposedly evolved to attract and accommodate the right pollinators.

 

Meadow rue

    This idea originated in the 1870s when Italian botanist Federico Delpino observed that certain types of flowers attracted particular kinds of pollinating animals—white sweet-scented night-opening flowers for moths, tubular red flowers for birds, musty-smelling flowers for bats. As the science of evolutionary biology developed during the 20th century, these observations developed into a theory supporting convergent evolution.

 

Fennel

     To explain why diverse, geographically separated plant species developed similar flower shapes, evolutionary biologists pointed to selective pressures from the groups of animals that pollinated those flowers. A plant that needed to attract pollinating bees, for example, would develop flowers that accommodate bees, whether the plant species grew in South Africa or New England.

 

Flat phlox flowers are convenient for bees

 
     This sounds right, and it’s nice to think of plant and animal species co-evolving to cooperate. More recent research hasn’t completely borne it out, though. A 2009 study of plants from six regions around the world showed that most flowers didn’t fit into the classical pollinator syndromes. Researchers also couldn’t predict the pollinators that would visit a flower based on the flower’s morphology. Some plants bank on attracting just one kind of pollinator, but many more are pollinated by a range of animals. Less exclusivity gives a plant population a more reliable chance to reproduce, even if one pollinator species has a bad year, or a bad decade.

 

Tubular flower of hummingbird sage

    Oh well, never mind. It’s still pretty amazing to zero in on the variety of flower shapes blooming in the garden now, despite the heat and drought. A lot of the flowers I’ve chosen recently for pollinators’ sake are daisy-shaped. In this group there are black-eyed Susans (Rudbeckia hirta), oxeye sunflowers (Heliopsis helianthoides), purple coneflowers (Echinacea purpurea), and zinnias (Zinnia elegans). 

 

Like others in the Aster family, oxeye sunflower has daisy-shaped blooms

     I observe these flowers attracting lots of bees and also some butterflies. They offer efficient foraging, because each daisy-shaped bloom is a composite of many tiny flowers, each offering nectar and pollen.

     But that’s hardly the only flower shape around. There are the flat umbels of fennel (Foeniculum vulgare), the spikes of spearmint (Mentha spicata), the prickly balls of globe thistle (Echinops bannaticus), the narrow tubes of hummingbird sage (Salvia guaranitica) and trumpet honeysuckle (Lonicera sempervirens), and the curved stems of goldenrod (Solidago spp.), which hold arrays of miniature daisy-shaped flowers.

 

Globe thistle

     Each of these flower shapes caters to a different group of pollinators. The hummingbird visiting the honeysuckle is at the large and dramatic end of the scale. More flowers in the garden are visited by diminutive native bees small enough to find the nectar in tiny flowers. The blooms offer nectar for a price, forcing pollinators to brush against pollen and carry it along. As a bee dips into the minuscule flowers of a coneflower’s central disc, it carries pollen from one to the next, enabling them to set seed.

 

A bee pollinates a purple coneflower