Keystone Species: Plants, Animals, and the Connections That Hold Ecosystems Together

The Mid-Atlantic sits at a biodiversity crossroads — northern forest species overlap with southern Coastal Plain communities across the Appalachians, Piedmont, and tidal shores. Native oaks support more caterpillar species here than anywhere else on the continent.

Keystone trees

Keystone perennials

In our plant database (3)

• Black Cherry (Prunus serotina) — A fast-growing native tree that ranks among the top five keystone plants in the eastern US. Hosts over 450 species of caterpillars.
• Butterfly Weed (Asclepias tuberosa) — A drought-tolerant milkweed with brilliant orange blooms. The only larval host plant for monarch butterflies.
• Northern Red Oak (Quercus rubra) — One of the most important keystone trees in eastern North America. Supports over 500 species of caterpillars alone.

The Southeast's longleaf pine savannas, Appalachian coves, and Coastal Plain wetlands harbor more plant species than almost anywhere else in North America. Native oaks, cherries, and willows provide the same keystone function here as in the North — but a richer understory layer adds milkweed, pawpaw, and spicebush to the food web.

Keystone trees

Keystone perennials

In our plant database (4)

• Black Cherry (Prunus serotina) — A fast-growing native tree that ranks among the top five keystone plants in the eastern US. Hosts over 450 species of caterpillars.
• Butterfly Weed (Asclepias tuberosa) — A drought-tolerant milkweed with brilliant orange blooms. The only larval host plant for monarch butterflies.
• Northern Red Oak (Quercus rubra) — One of the most important keystone trees in eastern North America. Supports over 500 species of caterpillars alone.
• Purple Coneflower (Echinacea purpurea) — An iconic prairie perennial with bold purple-pink daisy blooms. Long-lasting seedheads feed goldfinches through winter.

The Midwest transitions from the eastern deciduous forest to tallgrass prairie — the most biodiverse grassland ecosystem that ever existed in North America. Keystone oaks and willows anchor the forest edges; native sunflowers, goldenrod, and big bluestem anchor the prairie remnants.

Keystone trees

Keystone perennials

In our plant database (4)

• Black Cherry (Prunus serotina) — A fast-growing native tree that ranks among the top five keystone plants in the eastern US. Hosts over 450 species of caterpillars.
• Butterfly Weed (Asclepias tuberosa) — A drought-tolerant milkweed with brilliant orange blooms. The only larval host plant for monarch butterflies.
• Northern Red Oak (Quercus rubra) — One of the most important keystone trees in eastern North America. Supports over 500 species of caterpillars alone.
• Purple Coneflower (Echinacea purpurea) — An iconic prairie perennial with bold purple-pink daisy blooms. Long-lasting seedheads feed goldfinches through winter.

The Great Plains once supported the largest grassland ecosystem on Earth. Today it's among the most endangered. Keystone perennials — native sunflowers, goldenrod, gumweed, and prairie clover — support up to 89 specialist bee species each and are the foundation of grassland food webs.

Keystone trees

Keystone perennials

In our plant database (2)

• Butterfly Weed (Asclepias tuberosa) — A drought-tolerant milkweed with brilliant orange blooms. The only larval host plant for monarch butterflies.
• Purple Coneflower (Echinacea purpurea) — An iconic prairie perennial with bold purple-pink daisy blooms. Long-lasting seedheads feed goldfinches through winter.

The Rocky Mountain ecoregion spans dramatically different elevations — from dry sagebrush valleys to subalpine meadows and spruce-fir forests. Native willows dominate riparian corridors; aspen groves support the highest caterpillar diversity at mid-elevations.

Keystone trees

Keystone perennials

Our plant database is growing. Check back for species matched to this region.

The Pacific Northwest's maritime climate supports some of the most productive temperate rainforests on Earth. Native willows top the keystone rankings here; conifers (Douglas fir, western hemlock, Sitka spruce) support hundreds of caterpillar species in old-growth and second-growth forests.

Keystone trees

Keystone perennials

Our plant database is growing. Check back for species matched to this region.

California's Mediterranean climate is unique in North America — long dry summers, mild wet winters, and exceptional plant biodiversity. Native willows top the caterpillar rankings; coast live oak and valley oak support 270+ wildlife species. Ceanothus, found almost nowhere else, supports 120 caterpillar species.

Keystone trees

Keystone perennials

Our plant database is growing. Check back for species matched to this region.

The desert Southwest hosts a distinct and specialized native plant community adapted to heat, drought, and intense solar radiation. Native sunflowers support the most specialist bees of any plant genus in this ecoregion; desert willows and mesquite anchor riparian and wash habitats.

Keystone trees

Keystone perennials

Our plant database is growing. Check back for species matched to this region.