Over her career, Lucy Braun wrote four books and 180 articles published in over twenty journals. Her most remembered and lasting scholarly achievement was "Deciduous Forests of Eastern North America" (1950). Francis Fosberg said of her book "one can only say that it is a definitive work, and that it has reached a level of excellence seldom or never before attained in American ecology or vegetation science, at least in any work of comparable importance." The book was the culmination of her researches into vascular plant floristics and the composition of various deciduous forest plant communities, which had begun with her investigations of glaciated and unglaciated regions of southern Ohio. In the 1920s and 1930s, Braun's taxonomy work included a new catalog of the flora of the Cincinnati area, with a comparison to the flora of 100 years prior. Her study, one of the first of its kind for the United States, provided a model for analyzing changes to a flora over time. Building from the understanding that the southern Appalachian mountains were a refugium for communities of forest plants during intervals of glaciation, Braun proposed two migrations of prairie flora from the western grasslands during warming periods: a pre-Illinoian movement and a post-Wisconsinan one. She summarized her thinking in "The Phytogeography of Unglaciated Eastern United States and Its Interpretation". In the 1940s, Braun described as new to science four species and four varieties of vascular plants, all from localities in Kentucky, as well as a hybrid fern. On the whole, Lucy Braun is considered one of the most original thinkers in North American plant ecology from the first half of the twentieth century.