| Code | Definition | Number of Accessions |
| Atlantic Coastal Pine Barrens | Atlantic Coastal Pine Barrens | 18 |
| Blue Ridge | Blue Ridge | 2 |
| Central Appalachians | Central Appalachians | 5 |
| Central Corn Belt Plains | Central Corn Belt Plains | 7 |
| Eastern Corn Belt Plains | Eastern Corn Belt Plains | 1 |
| Eastern Great Lakes and Hudson | Eastern Great Lakes and Hudson Lowlands | 2 |
| Erie Drift Plain | Erie Drift Plain | 2 |
| Maine/New Brunswick Plains and | Maine/New Brunswick Plains and Hills | 6 |
| Middle Atlantic Coastal Plain | Middle Atlantic Coastal Plain | 2 |
| Mississippi Valley Loess Plain | Mississippi Valley Loess Plains | 1 |
| North Central Hardwood Forests | North Central Hardwood Forests | 2 |
| Northeast Coastal Zone | Northeastern Coastal Zone | 28 |
| Northern Appalachian Plateau a | Northern Appalachian Plateau and Uplands | 2 |
| Northern Appalachians and Atla | Northern Appalachians and Atlantic Maritime Highlands | 3 |
| Northern Lakes and Forests | Northern Lakes and Forests | 5 |
| South Central Plains | South Central Plains | 2 |
| Southeastern Plains | Southeastern Plains | 6 |
| Southeastern Wisconsin Till Pl | Southeastern Wisconsin Till Plains | 1 |
| Southern Michigan/Northern Ind | Southern Michigan/Northern Indiana Drift Plains | 5 |