Many botanical textbooks discuss “the” root as if it were a single entity. Such a unified treatment is justifiable given the seemingly stratified apices in roots of some ferns and reports of endodermal origins for lateral roots in some angiosperms. The roots of ferns and the roots of angiosperms, however, are distinct evolutionary innovations in two lineages from a common rootless ancestor. Given that convergence should result in all roots having similar biophysical or structural properties and similar expression of those genes useful in uptake and assimilation of minerals, where might a strong evolutionary signal be preserved? Perhaps in the physiological control of rhizogenesis? In the seed plants, auxin has been shown to control root formation in stem pieces, in root segments, and in whole plants; curiously, there seem to be no reports on the effects of auxin on root formation in ferns. My simple experiments with the leptosporangiate fern Ceratopteris find no evidence for an auxin stimulation of root formation from either root segments or leaf pieces, although they do show that high levels of auxin can inhibit both the formation of lateral roots from root segments and increases in the length of cultured roots. Sweeping conclusions require parallel experiments with eusporangiate and additional leptosporangiate ferns; these are are not yet complete. This work illustrates how an evo-devo context can frame physiological experiments.

Key words: evolution, ferns, roots