Environmental sex determination in response to light and biased sex ratios in Equisetum gametophytes

Summary 1 Sexual differentiation of Equisetum (horsetails) gametophytes is influenced by environmental conditions, and wild populations tend to be female biased. We show that photon irradiance has a very significant and reproducible effect on sex determination in three species of Equisetum grown in vitro. 2 Under our experimental conditions, high light levels (PAR = 24–48 µmol m−2 s−1) induce most gametophytes to differentiate as female, whereas only males are observed at PAR