A Thistle Banquet

On a recent walk through a local meadow I spotted a bank of Field Thistle (Cirsium discolor).

Field Thistle (Cirsium discolor)

It was eye-catching for two reasons.  The sight of the plant itself is arresting, with its tall candelabra-like shape topped with purple pompoms of flowers instead of candle flames.  But it was the sight of so many visitors to the flowers, often several on a single flower head, that was really breath-taking.  Bumble Bees, Honey Bees, Clearwing Moths and so many different butterflies moved quickly from flower to flower, pausing briefly to dine.  Field Thistle presents a sumptuous feast for potential pollinators!

At one ‘banquet table’, a Honey Bee, a Thistle Long-horned Bee (Melissodes desponsus) and a Hummingbird Clearwing Moth all dined amiably together.

A Honey Bee, a Thistle Long-horned Bee (Melissodes desponsus) and a Hummingbird Clearwing Moth all drinking nectar from Field Thistle (Cirsium discolor)

At another, several Bumble Bees, Honey Bees and Thistle Long-horned Bees shared a meal.

Bumble Bees, Honey Bees and a Thistle Long-horned Bee (Melissodes desponsus) feeding from Field Thistle (Cirsium discolor)

How is it that one flower head can accommodate so many visitors simultaneously?  Field Thistle is a member of the Aster or Composite (Asteraceae) family.  Each of the purple pompoms consists of a cluster of many long narrow tubular disk flowers.  You can see the individual flowers in the head in the lower part of the photo below.

Field Thistle (Cirsium discolor). Note the individual narrow, trumpet-like disk flowers shown below the bee.

The Long-horned Thistle Bee in the photo below is actively eating both pollen and nectar, and harvesting more to provision her nest for her larvae.  You can see the pollen she has collected packed onto hairs, called scopae, on her hind legs. We know this is a female, because only female bees harvest food for their offspring.  This bee species specializes on pollen from Field Thistle and a few other closely related plants (all of the genus Cirsium) for her larvae.  This makes her an excellent pollinator for Field Thistle, since she won’t be visiting other flowers.  It also means that without these thistles, this bee species would not survive.  It’s the same concept as the Monarch butterfly’s dependency on Milkweeds (Asclepias species) for survival, because Milkweeds are the only food their caterpillars can eat.

Thistle Long-horned Bee (Melissodes desponsus) feeding on Field Thistle (Cirsium discolor). She’ll bring the pollen on her hind legs to her nest. Note the pollen grains all over her body! Some will help with pollination.

Although it appears in the photos above that the various visitors to these flowers are happy to share the wealth of the Field Thistle banquet, I’m sorry to have to report that the Honey Bees actually indulged in bullying behavior.  They were especially hostile to the Thistle Long-horned Bees, trying to chase them away by bumping them.

Honey Bee bullying Thistle Long-horned Bee (Melissodes desponsus) on Field Thistle (Cirsium discolor).

Fortunately, the Thistle Long-horned Bees were undeterred.  They were also respectful of other diners, even those smaller than themselves.

The small bee (possible Eucera species) in the upper left is harvesting pollen. With Thistle Long-horned Bee (Melissodes desponsus) on Field Thistle (Cirsium discolor).

I visited this meadow several times within a few weeks, and each time there were at least a half dozen Hummingbird Clearwing Moths at the thistle.

Hummingbird Clearwing Moths on Field Thistle (Cirsium discolor).

Their close relative, a Snowberry Clearwing Moth, also stopped by for a drink.

Snowberry Clearwing Moth drinking nectar from Field Thistle (Cirsium discolor).

One of the Hummingbird Clearwing Moths shared a thistle banquet table with a female Zabulon Skipper, while a male Zabulon Skipper and Peck’s Skipper dined together at another.

Female Zabulon Skipper and Hummingbird Clearwing Moth drinking nectar from Field Thistle (Cirsium discolor).

Male Zabulon Skipper (left) and Peck’s Skipper drinking nectar from Field Thistle (Cirsium discolor).

These skippers are small butterflies who specialize on various grass species as food for their caterpillars.  Many of these grasses can be found nearby in the meadow.

Peck’s Skipper drinking nectar from Field Thistle (Cirsium discolor).

Peck’s Skippers were ubiquitous, sipping nectar alone and in the company of others, including Spicebush Swallowtails and Great-spangled Fritillaries.

Spicebush Swallowtail and Peck’s Skipper drinking nectar from Field Thistle (Cirsium discolor).

Two courting Great-spangled Fritillaries and Peck’s Skipper on Field Thistle (Cirsium discolor).

Eastern Tiger Swallowtails also visited the flowers for nectar.

Eastern Tiger Swallowtail drinking nectar from Field Thistle (Cirsium discolor).

All of these large butterflies specialize on plants found in the adjacent woodlands as food for their caterpillars.  Spicebush Swallowtails require Spicebush (Lindera benzoin), their namesake plant, or Sassafras (Sassafras albidum);  Great-spangled Fritillaries need violets; and Eastern Tiger Swallowtails use various tree species, including Ash (Fraxinus species), Tuliptrees (Liriodendrun tulipifera), and Black Cherry (Prunus serotina).

It was very encouraging to see that there were many Monarch butterflies partaking of the thistle feast.  Both Common (Asclepias syriaca) and Swamp Milkweed (Asclepias incarnata) were available in the meadow for egg-laying.

Monarch butterfly drinking nectar from Field Thistle (Cirsium discolor).

Even Ruby-throated Hummingbirds visited the thistles for nectar, but they didn’t stay long enough for a photo op.

Field Thistle’s strategy to protect itself from being eaten is to have very spiny leaves and branches.  This works well in deterring mammals from munching the plant; Field Thistle is not a species that deer are likely to browse.  But caterpillars are a different story.  Painted Lady butterflies as well as Common Loopers and some other moth species use this plant as food for their caterpillars.

Painted Lady on White Snakeroot (Ageratina altissima). Field Thistle (Cirsium discolor) is one of the plant species that Painted Lady butterflies can use as food for their caterpillars.

Common Looper Moth on New England Aster ( Symphyotrichum novae-angliae). Common Looper Moths caterpillars also eat the leaves of Field thistle (Cirsium discolor).

After all of this help with pollination, Field Thistle produces seed-like fruits called achenes.  They have a light, white fluff (called pappus) attached, enabling their dispersal by the wind. But these fruits are also desirable food and nesting material for Goldfinches and other birds.

Eastern Goldflinches harvesting seeds from Field thistle (Cirsium discolor)

Field Thistle is native from Saskatchewan to Quebec provinces in Canada and in much of the eastern half of the United States, although it is less common in the southeastern states and absent from Florida.  The flower color can vary from purple to pinkish, and is occasionally white.  Field Thistle is a biennial or short-lived perennial, replacing itself by producing seeds.  It can grow to a height of five to seven feet (1.5 – 2.1 meters).  Unlike some non-native thistles, Field Thistle is not invasive.

There is a non-native thistle, Bull Thistle (Cirsium vulgare), that closely resembles the native Field Thistle.  Some differences in their characteristics that can help tell them apart include:  Field Thistle leaves have consistently white felt-like or woolly undersides, Bull Thistle leaves are green to greenish-white below;  Bull Thistle has winged stems where the leaves meet them, Field Thistle does not;  Field Thistle usually has a ring of leaves pointing upward hugging the base of the inflorescence (flower head), like a very pointy stand-up collar, Bull Thistle may have one or two leaves below the inflorescence.

Field Thistle (Cirsium discolor) with great-spangled Fritillary butterfly. Note the stand-up leaf collar hugging the base of the flower head.

Field Thistle isn’t traditionally used in gardens, but in the right location in a sunny garden, it could really make a statement, and bring so many visitors!

Field Thistle (Cirsium discolor)


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Spicebush or Forsythia?


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Peterson, Roger Tory; McKenny, Margaret.  A Field Guide to Wildflowers of Northeastern and Northcentral North America. 1968.

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

Illinois Wildflowers

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Coralberry – A Winter Standout

Some plants are at their showiest in winter. Coralberry (Symphoricarpos orbiculatus), also called Indian Currant, is one of them.

Coralberry (Symphoricarpos orbiculatus) fruit

Coralberry (Symphoricarpos orbiculatus) fruit

Named for its fruit, Coralberry’s bright clusters of purplish to coral colored berry-like drupes persist on this shrub’s otherwise bare branches throughout much of the winter.  Drupes are fleshy fruits with seeds inside in a stony enclosure, like a peach.

Some plants have evolved to have their fruit be at its most appealing to their target seed dispersers (usually birds and some mammals) in late winter, when there is less food available. This strategy works well for the plants, since there is less competition from other food sources. It works for the animals, too, since it means they will have something to eat throughout the cold weather, tiding them over until the growing season begins.  Robins and Bobwhites are among the birds that consume Coralberry’s fruit.

American Robin

American Robin

From a human perspective, Coralberry’s fruit is not really recommended for consumption. It contains saponins, which give the fleshy fruit a bitter taste, and in sufficient (really large) quantities can be toxic. Saponins have antimicrobial and antifungal properties, in addition to some other potential medicinal applications. They likely help to protect the plant from invaders. Some Native American tribes made a decoction from the inner bark or leaves to use as a wash for weak, sore or inflamed eyes.

Coralberry grows to a maximum height of about 4 – 6 feet (1 – 2 meters) with gracefully arching branches. Its opposite leaves are typical of the Honeysuckle (Caprifoliaceae) family, of which Coralberry is a member.

Coralberry (Symphoricarpos orbiculatus) branch in summer

Coralberry (Symphoricarpos orbiculatus) branch in summer

You could walk past this shrub while it’s in bloom and never notice the flowers. They are small, bell-shaped, whitish, and completely concealed from above by leaves.  Fortunately, the bees, wasps and flies that are their likely pollinators are able to find them.  It flowers in mid-summer, usually July in the mid-Atlantic region.

Coralberry (Symphoricarpos orbiculatus) flowers and buds

Coralberry (Symphoricarpos orbiculatus) flowers and buds

A day-flying moth, the Snowberry Clearwing (Hemaris diffinis), has evolved to rely primarily on Coralberry and other members of the Honeysuckle family as food for its caterpillars, although they can also consume Dogbane (Apocynum species) leaves.

Snowberry Clearwing Moth (Hemaris diffinis)

Snowberry Clearwing Moth (Hemaris diffinis)

Snowberry Clearwing (Hemaris diffinis) caterpillar eating Japanese Honeysuckle

Snowberry Clearwing (Hemaris diffinis) caterpillar eating Japanese Honeysuckle

Snowberry Clearwings are named for their dependence on Coralberry and the closely related Snowberries (Symphoricarpos species) as caterpillar food plants. The Snowberries’ clusters of fruit are white, giving them their name.

The Hummingbird Clearwing (Hemaris thysbe) moth, another day-flier, also uses Symphoricarpos species, possibly including Coralberries, as food for its caterpillars. The Hummingbird Clearwing’s caterpillars have a somewhat broader palate, including hawthorns, cherries, plums and some viburnums in addition to the Snowberries.

Hummingbird Clearwing Moth (Hemaris thysbe) drinking nectar from Wild Bergamot (Monarda fistulosa)

Hummingbird Clearwing Moth (Hemaris thysbe) drinking nectar from Wild Bergamot (Monarda fistulosa)

Coralberry tolerates a wide range of soils, and grows in light conditions from partial shade to full sun. It reproduces through seed dispersal, with the assistance of birds or other animals that eat its fruit, and also through stolons, above ground runners that root where they touch the soil.  Its native range is primarily the eastern two-thirds of the United States, and parts of Utah.  It has also been introduced in Ontario province.

Winter is the time of year that Coralberry demands your attention. Look for its bright fruit along woodland edges and in open meadows.

Coralberry (Symphoricarpos orbiculatus) fruit

Coralberry (Symphoricarpos orbiculatus) fruit



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