Similar to lycophytes (Figure 1B) the stomata of gymnosperms (A) and ferns (B) do not open in response to low CO₂ in the dark and do not close at higher than ambient CO₂ concentration in the light.

<p>(A and B) Dynamic changes in stomatal conductance (black dots) in response to changes in ambient CO₂ concentration (thin solid line) in the dark and light (represented by black or white bars respectively at the bottom of the figure) in a representative gymnosperm <i>Ginkgo biloba</i> (A) and fern <i>Marsilea hirusta</i> (B). The dotted horizontal line represents stomatal conductance at ambient CO₂ concentration in the light. (C) Maximum stomatal conductances in the light overlapped broadly among all species, divided into lineages by vertical lines.