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

 

Pillars of the community

With winter approaching, most flowers have disappeared from the garden. One family of flowering plants, though, keeps on giving. Asteraceae, the aster family, competes with the orchids for the most populous of all plant families. Flowers for pollinators aren't the only ecosystem services they offer. Lettuce, dandelions, thistles, dahlias, zinnias, and marigolds are all members of this vast tribe.

 

Black-eyed Susans are in the Aster family

    Most flowers in this family are daisy-shaped, from the tiny flowers of goldenrod to huge sunflowers. An older name for the family is Compositae, because each blossom is a composite of many smaller flowers. What looks like a petal of a daisy flowers is actually an individual ray flower. The central disc, where the seeds develop, can comprise thousands of tiny flowers.

 

The central disc of a daisy offers multiple flowers for pollinators to visit

     Walking around the garden this week, I could still spot the brown and black flower heads of asters (Symphyotrichum spp.), black-eyed Susans (Rudbeckia hirta), coneflowers (Echinacea purpurea) and oxeye sunflowers (Heliopsis helianthoides), all North American natives in the Aster family. Flowers of sneezeweed (Helenium autumnale), another cousin, were still bravely opening after a hard frost earlier in the week. I aim to have something blooming for foraging insects throughout the growing season, but this perennial’s performance exceeds expectations.

Sneezeweed flowers opening

    It’s good to have these Aster family members in the garden because they offer a lot to insects and birds. The Lady Bird Johnson Wildflower Center recently zeroed in on the contributions of sunflowers to Texas’ ecology. Sunflowers don’t just provide plentiful nectar and pollen for pollinators and beneficial insects. Extrafloral nectar exuded from stems attracts ants. Beetle larvae over-winter in sunflower stalks. Even wide sunflower heads benefit wildlife by providing cover for quail and grouse chicks learning to forage for food.

Sunflowers offer both food and shelter for native insects-photo Pudelek

    Sunflowers may still be blooming in Texas. Here the blooms are gone. Massachusetts has fewer native sunflower species, but in the cold months it’s easy to observe birds feeding off seeds of daisy-shaped flowers of Asteraceae. In my yard, they like oxeye sunflower seeds and the fat seed heads of coneflowers. I haven’t seen any goldfinches lately—they’re not frequenting my thistle (nyjer) seed feeder--but if some stop by this winter, I hope to see them perching on the coneflower heads I’ve left standing.

    Of course, the Aster family isn’t exclusively altruistic. I notice how good the flowers are at recruiting passersby to transport seed to new locations. A pappus, a hairy or bristly structure, surrounds each fruit and helps it attach to fur or clothing or be wafted by the wind. Picture a dandelion head that releases its seeds to the breeze.

It's easy to see how thistle seeds hitch rides

    I’m determined to grow some annual sunflowers to maturity one of these years. So far my seedlings have consistently been bitten off at soil level before their stems get woody. I blame squirrels. 

A futile attempt to protect a sunflower seedling

I have a “pest-control pop-up,” a 3-foot tall tent made of fine mesh fabric on a flexible frame, that I hope to deploy next spring. Maybe if I sow the seeds and cover the area with the well-anchored tent, I can foil the dastardly sprout-eaters. Hope springs eternal.