The Atlantic Plain is a vast, flat, and surprisingly fragile global biodiversity hotspot.

Countries & Cities · Published 30 September 2026 Swipe more like this →

In short: Stretching thousands of miles from Cape Cod to the Mexican border, the Atlantic Plain is the flattest physiographic division in the United States. While often overlooked, this expansive region of sandy soil and wetlands is a critical biodiversity hub, harboring over 1,500 endemic plant species and unique fire-dependent ecosystems.

The Atlantic Plain is a massive physiographic division defined by its gentle seaward slope and sedimentary composition. It encompasses two primary provinces: the Coastal Plain, which sits above sea level, and the Continental Shelf, which extends beneath the ocean. This landscape is characterized by unlithified sediments—mostly sand and clay—that reach a maximum thickness of about 3 kilometers near Cape Hatteras, North Carolina. The region is remarkably low-lying, with most of its elevation remaining under 90 meters above sea level.

Ecologically, the plain is a paradox. Despite being nutrient-poor and primarily xeric, it supports an extraordinary array of life. It is now recognized as a global biodiversity hotspot, though it has suffered approximately 70% habitat loss. The region's longleaf pine savannas are particularly notable; these fire-dependent woodlands rely on periodic burns to prevent hardwood encroachment. In the south, the landscape shifts into the unique Everglades and Florida mangroves, the only Neotropical ecoregion in the continental United States.

The area's biological richness is bolstered by ancient refugia that have remained terrestrial since the late Cretaceous period, roughly 85 to 80 million years ago. This stability has allowed for high levels of endemism among amphibians and birds, including the Florida scrub jay and the red-cockaded woodpecker. While the boundary between land and sea is often indistinct—creating vast networks of bayous, marshes, and barrier islands—the underlying geological structure remains a consistent, gently dipping wedge of Mesozoic and Cenozoic deposits that define the eastern edge of the continent.

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