• Discover Life
• Flora of North America
• Tropicos
• USDA Plants Database
• World Wide Flowering Plants Family Identification

By Region

Northern Prarie
• USGS Northern Prarie Wildlife Research Center Western Wetland Flora Field Guide

Southeast

• Tennessee Valley Authority, Detailed Plant Search
• Trees of Alabama and the Southeast

Southwest

• Southwest Environmental Information Network Identification Keys

By State

Alabama

• Trees of Alabama and the Southeast
• Wildflowers of Alabama

Arizona


• Southwest Environmental Information Network Identification Keys

California


• Calflora
• California Academy of Sciences
• California Native Plant Society
• CalPhotos:Plants

Colorado


• Colorado Native Plants Society

Connecticut


• Connecticut Botanical Society

Delaware


• Deleware Wildflowers
• Delaware Wildfowers Violet Guide

Florida


• Atlas of Vascular Plants, Institute for Systemic Botany

Illinois


• Illinois Wildflowers

Missouri


• Missouri Botanical Garden
• Missouri Plants
• Missouri Wildflower Guide

Montana


• Montana Plant Life
• Montana Field Guide

Nevada
Nevada Natural Heritage Program

New Mexico

• Southwest Environmental Information Network Identification Keys

North Carolina

• Field and Swamp: Animals and Their Habitats
• Plant fact sheets NCSU

Oregon

• Native Plant Society of Oregon
• Oregon Flora Project

Texas

• Lady Bird Johnson Wildflower Center

Wyoming

• Malezas de Mexico (Weeds of Mexico)