A Small Beauty: Purple Milkwort

As we walked the path between the woods and the meadow at the Pole Farm section of Mercer Meadows, Wood Nymphs flitted in and out of the foliage, Monarchs flew by, some mating, and a Clouded Sulphur dipped into the path to lay eggs, the tip of her abdomen touching the leaves of White Clover for a split second each.

Monarch butterflies mating

Wood Nymph

Glancing down, I saw a small group of plants that at first glance looked like a type of clover.

Purple Milkwort (Polygala sanguinea).

But it wasn’t clover. The plants had narrow, alternate leaves, and the tiny flowers were tightly packed into a somewhat flat-topped cylindrical cluster.  It was Purple Milkwort (Polygala sanguinea).

In profile, the outside of the flowers in the cluster (inflorescence) look like overlapping scales, similar to those on a pine cone. These scale-like structures are sepals, the outermost appendage of a flower.  When present, sepals protect the other flower parts as they mature.  In Purple Milkwort, two sepals fuse to form these scale-like outer flower parts, each for a separate flower.

Purple Milkwort (Polygala sanguinea), with unknown insect, probably a beetle, investigating its flowers

Viewed from the top, the inflorescence looks like a single very showy flower.

Purple Milkwort (Polygala sanguinea)

A closer inspection tells a different story. The outermost layers of the display look like white petals dipped in purple, but they are the sepals visible when the flower cluster is viewed in profile.  Moving inward, there are tube-like structures, in luscious shades of yellow, peach and a deep bright pink, reminiscent of popsicle colors.  These tubes are the fused petals of the individual flowers that form this cohesive cluster. At the very center of the inflorescence is a bouquet of buds that have not yet opened.  Together these flowers and buds offer an impressive show.

Purple Milkwort (Polygala sanguinea). The fused petals form a tube, initially yellow, then fading to peach and deep pink.

What explains the different colors of the floral tubes? If you look carefully, the yellow flowers are closest to the center of the display.  They are the most recently in bloom, open for business, the bright yellow actively beckoning pollinators.  The peach flowers have been open longer, and are shutting down.  The deep pink flowers have been in bloom the longest, and are no longer seeking pollinators for themselves.   This kind of color change is usually a plant adaptation to direct pollinators only to the receptive flowers that have not yet been pollinated.  It makes the most efficient use of the pollinator’s efforts from the perspective of both the pollinator and the plant.  While the peach and pink flowers are not beckoning pollinators for themselves, they continue to add to the attractiveness of the overall floral display.

This brightly colored display works! It attracts small to medium sized bees and bee-flies with tongues long enough to reach down the floral tube for a nectar reward.  The photos below show a Sweat Bee (Halictid bee, Augochlorini tribe) exploring the flowers.

Sweat Bee (Halictid bee, Augochlorini tribe) exploring a Purple Milkwort (Polygala sanguinea) inflorescence

Sweat Bee (Halictid bee, Augochlorini tribe) positioning its proboscis for a drink from a Purple Milkwort (Polygala sanguinea) flower

Mmmm, delicious! Sweat Bee (Halictid bee, Augochlorini tribe) drinking nectar from a Purple Milkwort (Polygala sanguinea) flower

Purple Milkwort can be found in the ground cover layer of meadows, prairies, open fields and woods edges from Nova Scotia west to Ontario in Canada, and in much of the eastern two-thirds of the United States, except Florida. It can grow to a height of four to sixteen inches (1-4 dm).  Both the common and scientific names reflect the color of the flowers and the milky sap the plant contains.  The genus, Polygala, is derived from Greek words that mean ‘many or much’ and ‘milk’, referring to the sap.  The species, sanguinea, is derived from a word that means ‘blood’.  Other common names for Purple Milkwort are Blood or Field Milkwort, reflecting its color or habitat.  Although common, it’s not always easy to spot this little beauty.

Follow the camera lens to the Purple Milkwort in the shadows in the lower left of the photo.

Resources

Mauseth, James D. Botany An Introduction to Plant Biology.  2014.

Rhoads, Ann Fowler; Block, Timothy A. The Plants of Pennsylvania.  2007

Stearn, William T. Stearn’s Dictionary of Plant Names.  1996

Wilson, Joseph S.; Carril, Olivia Messinger. The Bees in Your Backyard. 2016.

Flora of Wisconsin

Illinois Wildflowers

Minnesota Wildflowers

USDA NRCS Plants Database

 

 

New England Asters – A Hotbed of Activity!

As the temperatures cool and the changing color of the leaves intensifies, plants in the Aster (Asteraceae) family continue to offer a bright display and food for flower visitors.

New England Asters (Symphyotrichum novae-angliae) with a flower fly (Eristalis transversa) and sweat bee (Agapostemom species)

New England Asters (Symphyotrichum novae-angliae) with a flower fly (Eristalis transversa) and sweat bee (Agapostemom species)

The Aster family is also called the composite family, because of the arrangement of their flowers. What looks to us like a single flower is actually a cluster of many flowers, often of two different types: ray flowers, which look like petals, and small tubular disk flowers in the center of the display.

Tricolored Bumble Bee (Bombus ternarius) feeding on New England Asters (Symphyotrichum novae-angliae)

Tricolored Bumble Bee (Bombus ternarius) feeding on New England Asters (Symphyotrichum novae-angliae)

Some aster family members, like dandelions (Taraxacum species), only have ray flowers.

Eastern-Tailed Blue butterfly drinking nectar from dandelion

Eastern-Tailed Blue butterfly drinking nectar from dandelion

Others have only disk flowers, like Mistflower (Conoclinium coelestinum).

Zabulon Skipper nectaring from Mistflower (Conoclinium coelestinum)

Zabulon Skipper nectaring from Mistflower (Conoclinium coelestinum)

In the case of New England Asters (Symphyotrichum novae-angliae), the ray flowers’ function is primarily to add to the attraction of the floral display to entice potential pollinators to visit the flowers.  It’s the tiny disk flowers at the center of each flower cluster that offer the reward of nectar and pollen.

Tricolored Bumble Bee (Bombus ternarius) feeding on New England Asters (Symphyotrichum novae-angliae)

Tricolored Bumble Bee (Bombus ternarius) feeding on New England Asters (Symphyotrichum novae-angliae)

Even on cool, blustery days, Bumble Bees, like the Tricolored Bumble Bee (Bombus ternarius) in the photo above, forage for food. The hair on their bodies helps to keep them warm, and is a good vehicle to pick up pollen from one flower and transfer it to another.

Sweat Bees are still active in autumn, fueled by the nectar aster family members offer.

Sweat bee (Halictid family)

Sweat bee (Halictid family)

Sweat bee (Agapostemom species) feeding from New England Aster (Symphyotrichum novae-angliae)

Sweat bee (Agapostemom species) feeding from New England Aster (Symphyotrichum novae-angliae)

Sweat bee (Agapostemom species) feeding from New England Aster (Symphyotrichum novae-angliae)

Sweat bee (Agapostemom species) feeding from New England Aster (Symphyotrichum novae-angliae)

Bees are not the only flower visitors at this time of year. Flies are second only to bees in their importance as pollinators.  Some species can be seen throughout fall.

Flower fly (Eristalis transversa) feeding from New England Aster (Symphyotrichum novae-angliae)

Flower fly (Eristalis transversa) feeding from New England Aster (Symphyotrichum novae-angliae)

Many fly species have evolved to look like bees or wasps in an effort to frighten off potential predators, but if you look carefully you can see the short antennae and very large eyes that almost meet in the center of their faces that are typical of flies.

Flower fly (Eristalis arbustorum) feeding from New England Aster (Symphyotrichum novae-angliae)

Flower fly (Eristalis arbustorum) feeding from New England Aster (Symphyotrichum novae-angliae)

The fly below is masquerading as a small wasp, hoping to elude predators.  It’s larvae consume aphids, another benefit from this diminutive creature!

Flower fly (Sphaerophoria contigua) on New England Aster (Symphyotrichum novae-angliae)

Flower fly (Sphaerophoria contigua) on New England Aster (Symphyotrichum novae-angliae)

Flower fly (Sphaerophoria contigua) on New England Aster (Symphyotrichum novae-angliae)

Flower fly (Sphaerophoria contigua) on New England Aster (Symphyotrichum novae-angliae)

Moths and butterflies also use New England Aster flowers as a convenient energy drink.

Common Looper Moth (Autographa precationis) feeding on New England Aster (Symphyotrichum novae-angliae)

Common Looper Moth (Autographa precationis) feeding on New England Aster (Symphyotrichum novae-angliae)

Despite their name, New England Asters are native throughout much of the United States and several Canadian provinces. They grow along roadsides and in meadows, and make a great addition to a sunny garden with average to moist soil, even tolerating clay soil.

Take a look at the New England Asters in the photo below. How many visitors can you find on these flowers?

New England Asters (Symphyotrichum novae-angliae) with flower visitors. How many can you find?

New England Asters (Symphyotrichum novae-angliae) with flower visitors. How many can you find?

 

Related posts

Asters Yield a Treasure Trove

Resources

Eaton, Eric R.; Kauffman, Ken. Kaufman Field Guide to Insects of North America.  2007.

USDA Plant Database

Missouri Botanical Garden

Illinois Wildflowers

 

Feasting on Green-headed Coneflower

How many flowers do you see in the photo below?

Gray Hairstreak on Green-headed Coneflower (Rudbeckia laciniata)

Gray Hairstreak on Green-headed Coneflower (Rudbeckia laciniata)

If you said one, that’s the answer I was looking for. However, it’s not correct!

The plant pictured here is Green-headed Coneflower (Rudbeckia laciniata), also sometimes called Cut-leaf Coneflower in deference to its deeply lobed leaves.  Green-headed Coneflower is a member of the Aster, or ‘Composite’ family, a name that’s pretty descriptive of their typical flower clusters (inflorescences). What our brains think is a single flower is actually a cluster (or composite) of tiny flowers, often of two different types, ray flowers and disk flowers. The petal-like parts of the flower cluster are each an individual ray flower with a single petal. In the center there are dozens of tiny tubular flowers called disk flowers, in reference to the disk-like shape of the flower cluster.  In the picture above, just a few of the disk flowers are blooming.

Some Aster family members just have ray flowers, like Dandelions.

Eastern-Tailed Blue nectaring on a Dandelion

Eastern-Tailed Blue nectaring on a Dandelion

Some have just disk flowers, like New York Ironweed.

Bumble Bee on New York Ironweed

Bumble Bee on New York Ironweed

Many, like Green-headed Coneflower, have both types of flowers. When both ray flowers and disk flowers are present, the ray flowers are often sterile, in which case their primary purpose is to act as nectar guides, alerting pollinators to the availability of nectar and pollen in the many disk flowers at the center of the flower cluster.

A Silver-spotted Skipper is nectaring on the disk flowers that are in bloom on this Green-headed Coneflower. The lowest disk flowers have finished blooming, while those at the top of the flower cluster are still in bud.

A Silver-spotted Skipper is nectaring on the disk flowers that are in bloom on this Green-headed Coneflower. The lowest disk flowers have finished blooming, while those at the top of the flower cluster are still in bud.

The disk flowers bloom gradually over a period of a few weeks, maximizing the plant’s chances for pollination with the assistance of insect partners. In the case of Green-headed Coneflower, the disk flowers bloom gradually from the bottom, or outside ring, to the top, or center, of the flower cluster.

A Red-banded Hairstreak is drinking nectar from the last few blooming flowers of this Green-headed Coneflower inflorescence.

A Red-banded Hairstreak is drinking nectar from the last few blooming flowers of this Green-headed Coneflower inflorescence.

Because of the number and size of its disk flowers, Green-headed Coneflower is able to attract many insects as potential pollinators. Often multiple insects can be found feeding simultaneously on different flowers in the same flower cluster.

This Green-headed Coneflower offers enough flowers with nectar to feed both an American Copper and a Honey Bee.

This Green-headed Coneflower offers enough flowers with nectar to feed both an American Copper and a Honey Bee.

Green-headed Coneflower’s disk flowers are large enough to accommodate small to medium sized butterflies like those pictured here.  They may rub against some pollen and transfer it to another plant, assisting with pollination.

Summer Azure with Green-headed Coneflower (Rudbeckia laciniata)

Summer Azure with Green-headed Coneflower (Rudbeckia laciniata)

Common Buckeye and Bumble Bee feeding on Green-headed Coneflower (Rudbeckia laciniata)

Common Buckeye and Bumble Bee feeding on Green-headed Coneflower (Rudbeckia laciniata)

Beneficial predators like the thread-waisted wasps (a species of Sphecid wasp) pictured below also benefit from the abundant nectar, giving them the energy they need to reproduce.  (I often see this species mating and nectaring at the same time, as they are doing here. A level of skill and coordination to which humans can only aspire!)  Their anatomy makes it more likely that they will help with pollination than butterflies, since more of their bodies are likely to come in contact with pollen.  The female wasps of this species (Eremnophila aureonotata) hunt caterpillars to feed their larvae.

Green-headed Coneflower with mating Wasps (Eremnophila aureonotata)

Green-headed Coneflower with mating Wasps (Eremnophila aureonotata)

But bees are the most likely to be successful pollinators, because they are the best anatomical match for gathering pollen, and it’s more likely to stick to the branched hair on their bodies and be carried away to be deposited on another flower.

Bumble Bee and American Copper nectaring on Green-headed Coneflower (Rudbeckia laciniata)

Bumble Bee and American Copper nectaring on Green-headed Coneflower (Rudbeckia laciniata)

Sweat Bee on Green-headed Coneflower (Rudbeckia laciniata)

Sweat Bee on Green-headed Coneflower (Rudbeckia laciniata)

The Sweat Bee below is gathering pollen on her hind legs to take back to feed her larvae.  Only female bees gather pollen this way.

Sweat Bee (Lasioglossum species) on Green-headed Coneflower (Rudbeckia laciniata)

Sweat Bee (Lasioglossum species) on Green-headed Coneflower (Rudbeckia laciniata)

Dining on Green-headed Coneflower is not without danger, as this Bumble Bee found out when it fell victim to a Wheel Bug, a type of assassin bug.  Sometimes the diner becomes the dinner.

Wheel Bug (Arilus cristatus) consuming a Bumble Bee smoothie

Wheel Bug (Arilus cristatus) consuming a Bumble Bee smoothie

If the flowers are successfully pollinated, you’re likely to see Goldfinches and other birds feeding on the seeds later in the season and throughout fall.

Goldfinch eating Green-Headed Coneflower seeds

Goldfinch eating Green-Headed Coneflower seeds

The Aster family is the second largest family of flowering plants in terms of its number of species, second only to the Orchid family.  In late summer and fall the Aster family represents a high percentage of what’s in bloom.  For information on a few other Aster family members, see Asters Yield a Treasure Trove! and Fall Allergies?  Don’t Blame Goldenrod!

Resources

Eaton, Eric R.; Kauffman, Ken.  Kaufman Field Guide to Insects of North America.  2007.

Elpel, Thomas J.  Botany in a Day.  2006.