Keystone Plants: Flowering Perennials in Ecoregion Five

Author: Claire McCaughey, Master Gardeners of Ottawa-Carleton; published with permission.

“We can each make a measurable difference almost immediately by planting a native nearby. As gardeners and so empowered, and the stakes have never been so high.”

Bringing Nature Home , Douglas Tallamy

By now, having followed the first three parts of our series on keystone plants in Ecoregion Five (Northern Forests), it will surely be evident to readers that keystone plants are vital to the ecosystem in supplying food to specialist native bee species and acting as host plants for young caterpillars of butterfly and moth species. Keystone trees and shrubs play this vital role while also supplying the bones of the garden over the long term. Most, if not all, of the genera of trees and shrubs are well known. In the fourth and last part of the series, we turn our attention to keystone flowering perennials.

A New Appreciation for Some Old Friends Among the genera of keystone flowering perennials in Ecoregion 5, some are quite familiar to gardeners. These include Rudbeckia hirta (black-eyed Susan), Coreopsis lanceolata (lance leaf coreopsis), and Symphyotrichum novae-angliae (New England asters). Though gardeners may know these worthy native plants, they may not realize that these species and others in the same genera are keystone plants of Ecoregion 5 and therefore have an important function in the landscape that is critical to the food web and wildlife.

However, it is important to note that popular cultivars of the above-mentioned plants do not serve as keystone plants, only the species (e.g., Symphyotrichum novae-angliae rather than a cultivar of S. novae-angliae such as ‘Purple Dome’). Both Rudbeckia hirta and Coreopsis lanceolata are considered short-lived perennials. Coreopsis should be deadheaded often to promote blooming.

Ecosystem Gold

Also recognized as a familiar genus of plants, Solidago (goldenrod). Though tall goldenrods may be the bane of some gardeners due to their aggressive seeding and weedy appearance, the three keystone species (Solidago canadensis, S. nemoralis, and S. gigantea) are considered a powerhouse among keystone perennials, functioning as host plants to 120 caterpillar species and supplying pollen for 22 specialist bee species. It is worth reminding readers that goldenrod does not cause allergies.

Discovering New Plants and Their Function

The list of keystone flowering perennials (see below) includes two plants I had never heard of as a gardener until doing research for this article. Cirsium muticum (swamp thistle) is a taller plant (up to 1 m) with purple flowers, and being a thistle is prickly. Verbesinia alternifolia (wingstem) is a very tall (1.5 m), yellow-flowered plant flowering late in the season. These two may not necessarily be plants that you would choose to plant in a small urban garden, but it is important to learn to identify these plants because of their value in the ecosystem for birds as well as caterpillars and bees. If you have a larger rural property, you may already have these plants on your property without knowing it.

Using Keystone Flowering Perennials in the Landscape

Keystone perennials will look best incorporated into a naturalistic or natural garden design when combined with other native plants and grasses. It is useful to look at how these plants grow in the wild. Which plants grow together in plant communities? Which plants tend to grow in small clumps or individually, and which grow in drifts?

Though all keystone perennials have value, some species will be easier to add to your landscape design, especially in a small urban garden. For example, grey goldenrod (Solidago nemoralis) is a shorter species of the Solidago genus (30 cm). It also has the benefit of flowering later in the season, from late August into September. If you already have the taller species of goldenrod (Solidago canadensis, S. gigantea), do not remove them but consign them to the very back of your garden if you are concerned about a weedy look to your garden.

Most of these keystone plants flower later in the season, so consider planting them in an area with full sun where they can be seen and appreciated in flower. If you have a shadier garden, you may want to consider other native plants that will work better in lower light conditions.

Keystone Flowering Perennials to Look for This Spring

There is no time like the present to do something positive for our ecosystems and for biodiversity; therefore, consider trying to grow one or more of these keystone species this year.

• S. lateriflorum (calico aster),
• Symphyotrichum novae-angliae (New England Aaster),
• S. puniceum (swamp aster)
• Helianthus strumosus (pale leaf sunflower),
• H. decapetalus (thin-leaf sunflower)
• Solidago canadensis (Canada goldenrod),
• S. nemoralis (grey goldenrod),
• S. gigantea (giant goldenrod)
• Rudbeckia hirta (black-eyed Susan),
• R. laciniata (green-headed coneflower)
• Coreopsis lanceolata (lance leaf coreopsis),
• C. tinctoria (plains coreopsis)
• Grindelia squarrosa (curly cup gumweed)*
• Bidens cernua (nodding bur marigold),
• B. tripartita (three-lobe beggarticks)
• Cirsium muticum (swamp thistle)
• Verbesina alternifolia (wingstem)

Note that two of the plants listed with an asterisk above are identified in VASCAN (the comprehensive database of vascular plants in Canada) as introduced plants to Ontario (https://data.canadensys.net/vascan/about).

Some of these perennials will be easier to find than others. However, specialist native plant nurseries and growers will have most as small plant plugs. Also, plan for next year and consider growing some of these plants from seed using the winter sowing method. In the last few years, more local sources of native plant seeds have become available.

Other Native Flowering Plants for Specialist Bees

Though they are not considered keystone species, keep in mind that there are at least thirty other flowering perennial genera that specialist bees rely upon. These include, among others, Erigeron (fleabane), Ratibida (prairie coneflower), Vernonia (ironweed), Dalea (prairie clover), Echinacea (coneflower), and Lupinus (lupin). These could be included in your naturalistic garden design along with the keystone species.

Note: The map Ecoregions of North America – level I, was used to determine the ecoregion for the keystone plant articles. This is a large-scale map, and boundaries are not always clear or clean.