A keystone plant is a native species with a disproportionately large effect on its ecosystem. The term comes from architecture, where a keystone holds an entire arch together; without it, the arch collapses. Similarly, removing a keystone plant can cause a significant decline in biodiversity and unravel an ecosystem’s stability. These plants are defined not by their abundance, but by their powerful role in sustaining the life around them.
The Ecological Role of Keystone Plants
The primary role of a keystone plant is to serve as a foundational food source for the insects that have evolved alongside them. Most plant-eating insects have developed highly specialized relationships with just one or a few native plant lineages. They have adapted to overcome the specific chemical defenses of their host plants, rendering them unable to digest other species. Research by entomologist Dr. Doug Tallamy has shown that a small percentage of native plants, the keystones, support the vast majority of local butterfly and moth populations.
These insects, particularly caterpillars, are a concentrated source of protein and fats. They are a primary food source for many other animals, creating a link in the food web that channels energy from plants to other organisms. This connection is important for terrestrial birds, 96% of which rely on insects to feed their young. A pair of nesting chickadees, for instance, must find between 6,000 and 9,000 caterpillars to successfully raise one clutch of chicks.
Without robust populations of keystone plants, there would not be enough caterpillar food to sustain local bird populations, leading to negative effects throughout the ecosystem. Specialist bees also depend on these plants. Many native bee species are pollen specialists, meaning they can only feed their young with pollen from specific native plants. The presence of keystone species ensures these pollinators can survive and continue their work, which benefits countless other plants, including many food crops.
Common Keystone Plant Genera
Among the most powerful keystone plants across North America are several genera of trees and perennials known for supporting a high diversity of life. Oaks, belonging to the genus Quercus, are highly significant. In many regions of the United States, native oaks can support over 500 different species of caterpillars, making them ecological powerhouses. They provide not only food but also shelter and habitat for a wide array of wildlife.
Other effective keystone trees include willows (Salix) and the group containing native cherries and plums (Prunus). Willows are particularly important in northern climates and can host hundreds of caterpillar species, while cherries are valuable nationwide. Birches (Betula) are another major contributor, supporting over 400 species of Lepidoptera (butterflies and moths). These woody plants form the backbone of many terrestrial food webs.
In the realm of herbaceous perennials, goldenrods (Solidago), asters (Symphyotrichum), and perennial sunflowers (Helianthus) are standouts. Goldenrods alone can serve as host plants for over 100 caterpillar species and provide pollen for dozens of specialist bee species. Asters and sunflowers also support a significant number of both caterpillars and specialist bees, making them valuable additions to any landscape aiming to boost local biodiversity.
Identifying Keystone Plants for Your Region
A plant’s value as a keystone is dependent on its native range; a plant that is a powerhouse in one ecoregion may be of little use in another. Identifying which keystone plants are native to your specific area is an important step. The most direct tool for this is the National Wildlife Federation’s Native Plant Finder. This online resource allows users to enter their zip code to generate a ranked list of native trees, shrubs, and perennials for attracting butterflies and moths in their locality.
The database, built on the research of Dr. Doug Tallamy, prioritizes plants based on the number of caterpillar species they host, providing a clear guide for making high-impact choices. The lists generated by the finder specify the plant genera, such as Quercus for oaks or Solidago for goldenrods, that are most productive in that particular zip code. This allows for focused and effective planting.
Beyond this primary tool, gardeners can find more localized information through other channels. State-level native plant societies and local university extension offices are excellent sources of regional expertise. These organizations often publish their own guides, plant lists, and articles tailored to the specific conditions and ecosystems within the state.
Incorporating Keystone Plants into a Landscape
Adding keystone plants to a property does not require a complete and costly overhaul of an existing landscape, as even small changes can have a meaningful ecological impact. A simple starting point is to replace a non-native ornamental shrub with a native keystone variety. For those with lawn space, adding a single keystone tree, such as a native oak or cherry, can create a habitat that will support wildlife for decades.
For homeowners with limited space, such as a patio or balcony, container gardening offers a viable path for contributing. Many keystone perennials, like asters, coneflowers, or even some smaller shrubs, can thrive in pots. This approach makes it possible for anyone to provide resources for local pollinators and insects.
The goal is to begin weaving these ecologically productive plants back into the landscape, even one plant at a time. Consider the different layers of a garden—from groundcovers to shrubs to trees—and try to include a keystone species in each layer where possible. Allowing seed heads to remain through the winter provides food for birds, and leaving fallen leaves as mulch offers shelter for overwintering insects.