He was born on a small heathland farm, named Raunkiær, in Lyhne parish in western Jutland, Denmark.

He was married to the author and artist Ingeborg Raunkiær (1863–1921), who accompanied him on journeys to the West Indies and the Mediterranean and made line drawings for his botanical works.

Raunkiær devised a system for categorising plants by life-form as a way of ecologically meaningful comparison of species and vegetation in regions having different floras.

[3] As a further experiment in characterizing plant communities, Raunkiaer devised a numerical scheme based on leaf size classes and leaf type (simple or compound) that was extended by L. J. Webb[4] and is used as a way to classify forest types more simply than by lists of component species.

[5][6][7] Farley Mowat, in his book, Never Cry Wolf, described using a Raunkiær's Circle in making a "cover degree" study to determine the ratios of various plants one to the other.