Om Skudbygning, Overvintring og Foryngelse.

The classification was based on his meticulous observations while raising wild plants from seed in the Copenhagen Botanical Garden. Fourteen informal groups were recognized, based on longevity of the plant, power of vegetative propagation, duration of tillers, hypogeous or epigeous type of shoots, mode of wintering and degree and mode of branching of rhizomes.

Johannes Eugenius Warming (1841–1924), commonly known as Eugen Warming, was a pioneering Danish botanist widely recognized as one of the founding figures of modern ecology. He authored the first textbook on plant ecology in 1895, introduced the first university course in the subject, and helped define the scope and content of ecological science. In 1975, ecologist R. J. Goodland asserted: “If one individual can be singled out to be honoured as the founder of ecology, Warming should gain precedence” ("The Tropical Origin of Ecology: Eugen Warming's Jubilee"). Warming wrote a number of textbooks on botany, plant geography and ecology, which were translated to several languages and were immensely influential at their time and later. Most important were “Plantesamfund and Haandbog i den systematiske Botanik”.