Where do Winterberries Come From?

It’s difficult to walk past Winterberry Holly (Ilex verticillata) when it’s in fruit without noticing it.  The abundant, vividly red, globular, fleshy fruits of this aptly named shrub never fail to catch the eye.  

Winterberry Holly (Ilex verticillata) in fruit
Winterberry Holly (Ilex verticillata) in fruit

Where do all of those luscious-looking fruits come from?  

Have you ever noticed Winterberry Holly in bloom?

In late spring, Winterberry Holly is covered with an equally large number of somewhat inconspicuous greenish-white flowers. The flowers bloom gradually over a period of a few weeks. 

Like all hollies, Winterberry usually has male and female flowers on separate plants. Only female flowers can develop fruit. Although it isn’t typical, there may occasionally be a specimen with male and female flowers on the same plant, or some flowers that are perfect, that is, they have both male and female parts. Plants often have some variation, as they continue to evolve to try to find the most effective and efficient survival strategies.

Female flowers are usually in small clusters of up to three. The flowers have a single pistil (the female reproductive part) at their center. The green rounded base of the pistil is the ovary. If a flower is successfully pollinated, the ovary will mature, becoming the bright red fruit we see later in the season. The ovary is topped by a stigma, where pollen must be deposited in order for pollination to occur and fruit to develop.

Winterberry Holly (Ilex verticillata) female flowers in bloom.  The whitish specks on the branches are lenticels, through which the plant exchanges gases with the surrounding atmosphere. Lenticels are commonly seen on Winterberry holly branches.
Winterberry Holly (Ilex verticillata) female flowers in bloom. The whitish specks on the branches are lenticels, through which the plant exchanges gases with the surrounding atmosphere. Lenticels are characteristic of Winterberry holly branches.

The white arrow- or spade-shaped projections in between the petals of the female flowers are sterile stamens; they don’t produce pollen that can fertilize the flowers.  It’s likely that they help attract pollinators. As these sterile stamens age, they turn brown.

Winterberry Holly (Ilex verticillata) female flowers in bloom.  The female reproductive part, the pistil, is the green mound-shaped object in the center of the flower.  The ovary is at the base, and will develop into a fruit if pollination is successful and the ovules inside are fertilized. The flat-ish tissue at the top is the stigma, where pollen must be placed by an incoming bee or other pollinator.  The white arrow- or spade-shaped projections in between the petals are sterile stamens.
Winterberry Holly (Ilex verticillata) female flowers in bloom. The female reproductive part, the pistil, is the green volcano-shaped object in the center of the flower. The ovary is the base of the volcano, and will develop into a fruit if pollination is successful and the ovules inside are fertilized. The flat-ish tissue at the top is the stigma, where pollen must be placed by an incoming bee or other pollinator. The white arrow- or spade-shaped projections in between the petals are sterile stamens.

Male flowers often bloom in crowded clusters of up to 10 or more.  The male reproductive parts, called stamens, reach upward from the face of the flower, the anthers at their tips ready to deposit pollen on a flower visitor.   

Winterberry Holly (Ilex verticillata) male flowers, blooming in densely-packed clusters.
Winterberry Holly (Ilex verticillata) male flowers, blooming in densely-packed clusters.
Winterberry Holly (Ilex verticillata) male flowers in bloom. The male reproductive parts, called stamens, reach up from the face of the flowers.  Pollen is produced from the anthers at their tips.
Winterberry Holly (Ilex verticillata) male flowers in bloom. The male reproductive parts, called stamens, reach up from the face of the flowers. Pollen is produced from the tan anthers at their tips.

Winterberry Holly needs third party assistance to move pollen from a male flower on one plant to a female flower on another plant, in order to achieve pollination. It may be easy for people to walk past without noticing when these shrubs are in bloom, but fortunately the flowers are enticing beacons to potential pollinators of many different species, especially bees. A recent study showed Winterberry Holly to be among the most attractive to bees of the flowering shrubs.

In my own garden I spotted Bumble Bees, Mining Bees, Sweat Bees, Small Carpenter Bees and a wasp visiting the flowers for nectar rewards. Bees also eat pollen, and female bees may collect pollen to feed their larvae.

Confusing or Perplexing Bumble Bee (Bombus perplexus) visiting a Winterberry Holly (Ilex verticillata) female flower.
Confusing or Perplexing Bumble Bee (Bombus perplexus) visiting a Winterberry Holly (Ilex verticillata) female flower.
Mining Bee with a Winterberry Holly (Ilex verticillata) flower.
Mining Bee drinking nectar from a Winterberry Holly (Ilex verticillata) flower.
Sweat Bee with a Winterberry Holly (Ilex verticillata) female flower.
Sweat Bee visiting a Winterberry Holly (Ilex verticillata) female flower.
Small Carpenter Bee (Ceratina species) departing from a Winterberry Holly (Ilex verticillata) flower.
Small Carpenter Bee (Ceratina species) departing from a Winterberry Holly (Ilex verticillata) female flower.
Eastern yellow Jacket drinking from a Winterberry Holly (Ilex verticillata) female flower.
Eastern Yellow Jacket drinking from a Winterberry Holly (Ilex verticillata) female flower.

Without the assistance of these flower visitors, pollination would not take place, no fruit would develop, and Winterberry Holly would not be able to reproduce. If these pollinators do the job the plants have enticed them to do, fruit develops, ripening by fall.

Winterberry Holly (Ilex verticillata) in fruit.
Winterberry Holly (Ilex verticillata) in fruit.

Birds are the primary target audience for the colorful display of Winterberry Holly’s bright red fruit. Many different species of birds including Eastern Bluebirds,

Eastern Bluebirds enjoy Winterberry Holly (Ilex verticillata) fruit
Eastern Bluebirds enjoy Winterberry Holly (Ilex verticillata) fruit

White-throated Sparrows,

White-throated Sparrows are among the birds that eat Winterberry Holly (Ilex verticillata) fruit.
White-throated Sparrows are among the birds that eat Winterberry Holly (Ilex verticillata) fruit.

and Hermit Thrush

Hermit Thrush sitting in a Winterberry Holly (Ilex verticillata)
Hermit Thrush in a Winterberry Holly (Ilex verticillata)

eat the fleshy fruit and later become the unwitting dispersers of the seeds inside as they deposit them with natural fertilizer when defecating.

Small mammals like mice and squirrels may eat Winterberry fruit, too. People are just the accidental beneficiaries of the bright spectacle, but shouldn’t eat the fruit, which is toxic to humans.

Winterberry Holly fruits contain more carbohydrates than fats, making them less preferred by birds than some other fruit available in the fall. As a result, Winterberry fruit is frequently passed over until later in the season, often well into winter, although sometimes a flock of hungry American Robins or Cedar Waxwings will strip a Winterberry Holly of all its fruit in a matter of hours.

American Robin in Winterberry Holly (Ilex verticillata).  A flock of hungry Robins can strip a shrub of its fruit in a matter of hours.
American Robin in Winterberry Holly (Ilex verticillata). A flock of hungry Robins can strip a shrub of its fruit in a matter of hours.

Winterberry Holly is a deciduous shrub or understory tree that grows to a maximum height of about 15 – 20 feet (5 – 6 meters). It prefers moist soil, and is indigenous in bogs and wet woods in the eastern half of the United States and Canada. It makes a great addition to your own landscape for its benefit to pollinators, birds and other wildlife. It doesn’t hurt that Winterberry Holly adds some bright color to a winter landscape.

Winterberry Holly (Ilex verticillata) in fruit.
Winterberry Holly (Ilex verticillata) in fruit.

Resources

Eastman, John.  The Book of Swamp and Bog.  1995.

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

Mach, Bernadette M.; Potter, Daniel A. Quantifying bee assemblages and attractiveness of flowering woody landscape plants for urban pollinator conservation. 2018.

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

Williams, Paul; Thorp, Robin; Richardson, Leif; Colla, Sheila. Bumble Bees of North America. 2014.

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

Illinois Wildflowers

Minnesota Wildflowers

Missouri Botanical Garden Plant Finder

USDA NRCS Plant Database

Embracing the Shade: Summer and Fall

Is it possible to have a perennial shade garden with continuous bloom throughout the summer and fall?  By June, the trees are fully leafed out, sheltering our home from the summer sun’s strong rays. That means that the garden is in the shade, too. Will anything be blooming? You bet.

Spicebush Swallowtails nectaring on Bottlebrush Buckeye

Spicebush Swallowtails nectaring on Bottlebrush Buckeye

Some spring bloomers, like Heartleaf Foamflower (Tiarella cordifolia) and Virginia Goldenstar (Chrysogonum virginianum), also called Green and Gold, may continue their display into the summer months. While not yet blooming, the leaves of White Wood Aster (Eurybia divaricata) join the violets, ferns, and Spreading Sedge (Carex laxiculmis) to form a ground cover blanketing much of the garden. Arching four to five feet above them are long sprays of Goat’s-beard (Aruncus dioicus) a.k.a. Bride’s Feathers’ tiny white flowers, lighting up the deep shade. June brings Rosebay Rhododendron (Rhododendron maximum) and Wild Hydrangea (Hydrangea arborescens) blossoms, too.

Bottlebrush Buckeye (Aesculus parviflora) is part of the shrub layer in the woods behind our house. In July, this reliable bloomer with its large palmately compound leaves and tall spikes of white tubular flowers attracts Ruby-throated Hummingbirds in addition to Spicebush and Eastern Tiger Swallowtails.

Dark form Eastern Tiger Swallowtail nectaring on Bottlebrush Buckeye

Dark form Eastern Tiger Swallowtail nectaring on Bottlebrush Buckeye

Last summer we were surprised to see dark morph Tiger Swallowtails nectaring on the Bottlebrush Buckeye. By adopting this Pipevine Swallowtail-like coloration disguise, the Tiger Swallowtails gain some protection from being eaten by birds and other predators who have learned of the Pipevine Swallowtail’s toxicity. The dark morph occurs most frequently in areas where Pipevine Swallowtails are present. Maybe Dutchman’s Pipevine (Aristolochia macrophylla) and its namesake swallowtail are increasing in our area!

Courting Zabulon Skippers on Purple Giant Hyssop

Courting Zabulon Skippers on Purple Giant Hyssop

July is also the beginning of Purple Giant Hyssop’s (Agastache scrophulariifolia) long bloom, lasting well into September. We have it in both deep shade and a spot that gets a few hours of afternoon sun, blooming dependably in both locations. This herbaceous plant is a great choice for a woodland garden, with a growth form that is similar to Butterfly Bush. In our garden, butterflies from the smallest skippers to the largest swallowtails love Purple Giant Hyssop. Bees love it, too, and even hummingbirds may drink from the nectar-packed purple flowers.

Eastern Tiger Swallowtail nectaring on Purple Giant Hyssop

Eastern Tiger Swallowtail nectaring on Purple Giant Hyssop

Pollinators can’t resist Mountain Mints.

Sweat Bee (Lasioglossum species) on Short-toothed Mountain Mint

Sweat Bee (Lasioglossum species) on Short-toothed Mountain Mint

I decided to try Short-toothed Mountain Mint (Pycnanthemum muticum), also called Clustered Mountain Mint, the only one of the Mountain Mint (Pycnanthemum) species I thought could tolerate some shade. I put it in the one location that gets about four hours of afternoon sun, and I got lucky. While not as robust as it would be in a sunnier spot, it’s doing well, its tiny magenta and white blossoms enticing the smaller butterflies like azures and skippers throughout July and August.

Summer Azure nectaring on Short-toothed Mountain Mint

Summer Azure nectaring on Short-toothed Mountain Mint

As summer progresses, False Sunflower (Heliopsis helianthoides) radiates bright yellow sunbursts at the wood’s edge from July well into September.

Sweat Bee (Agapostemom species) on False Sunflower (Heliopsis helianthoides)

Sweat Bee (Agapostemom species) on False Sunflower (Heliopsis helianthoides)

Eastern Tiger Swallowtails and Bumble Bees are frequent diners at Great Blue Lobelia (Lobelia siphilitica), open for business during August and September.  Even Ruby-throated Hummingbirds will stop here for a drink.

Eastern Tiger Swallowtail nectaring on Great Blue Lobelia

Eastern Tiger Swallowtail nectaring on Great Blue Lobelia

Also in August, after gathering energy from the sun from the earliest spring days when its leaves begin to emerge, White Wood Aster blinks on its light show of white blossoms, illuminating the dense shade through October. The delicate blue disk flowers of Carolina Elephantsfoot (Elephantopus carolinianus) provide a complementary offset in August and September.

White Wood Aster

White Wood Aster

Butterfly traffic slows by September, but Black Swallowtails may still lay eggs this late, sometimes on my cooking herbs (parsley and dill).

Black Swallowtail caterpillar eating parsley

Black Swallowtail caterpillar eating parsley

Last fall we hosted a chrysalis on a hot pepper plant.

Black Swallowtail chrysalis on pepper plant

Black Swallowtail chrysalis on pepper plant

More aster family members begin their fall performance now, including Blue Wood Aster (Symphyotrichum cordifolium),

Blue Wood Aster with Bumble Bee

Blue Wood Aster with Bumble Bee

Wreath Goldenrod (Solidago caesia),

Wreath Goldenrod

Wreath Goldenrod

and Zigzag Goldenrod (Solidago flexicaulis), in bloom and offering nectar through October or early November. Like White Wood Aster, all of the foliage of these species emerged in early spring from the winter’s leaf cover.

All of these summer and fall blooming species have a reproductive strategy that includes clusters or spikes of flowers that bloom gradually over a period of many weeks, increasing each plant’s chances of pollination by bees, butterflies, and others, and resulting in a long colorful garden display.When successfully pollinated, Purple Giant Hyssop, Carolina Elephantsfoot and Woodland Sunflower offer Chickadees, Goldfinches and other birds a fall bounty of food.

Goldfinch eating Elephant's Foot seeds

Goldfinch eating Elephant’s Foot seeds

Resident and migrant birds dine on the bright red fruit of Spicebush (Lindera benzoin) and Flowering Dogwood (Cornus florida) and the dark blue fruit of Sassafras (Sassafras albidum) and Blackhaw Viburnum (Viburnum prunifolium). This is after a busy season of acting as caterpillar food plants – Spicebush and Sassafras for Spicebush Swallowtails, Flowering Dogwood and Blackhaw for Spring Azures.

Flowering Dogwood fruit

Flowering Dogwood fruit

In October and November, Witch-hazel’s (Hamamelis virginiana) spidery yellow blossoms complement the fall foliage.

Witch-hazel flowers and fruits

Witch-hazel flowers and fruits

The bright red fruits of Winterberry Holly (Ilex verticillata) may last until late winter, when hungry birds finally eat them.

Winterberry Holly berries

Winterberry Holly berries

Little maintenance is required in this woodland garden. Because the plants have filled in to form a ground cover in most places, there is little weeding to do. We primarily use naturally fallen leaves as mulch, although we may supplement with a bit of prepared leaf compost around the front edges, in deference to our homeowners’ association’s sensibilities.

When we were trying to grow lawn in the shade, it was sparse, and we had problems with standing water after a heavy rainfall. Not anymore. The trees, shrubs and other plants in the garden, as well as the leaf litter, help the soil to absorb rainfall. The shade keeps the soil from drying out too quickly. So once these plants are established, watering is only required when drought conditions become extreme.

Not a bad performance for a woodland garden. And it brings so much pleasure!

Notes:

This is part 3 of a 3 part series.  To see parts 1 & 2, see A Butterfly Garden That Embraces the Shade and  A Butterfly Garden That Embraces the Shade – Spring.

This post was adapted from an article that was originally published in the Summer 2013 issue of Butterfly Gardener, a publication of the North American Butterfly Association.