Ultrastructural Basis and Developmental Control of Blue Iridescence in Selaginella Leaves

The iridescent blue color of several Selaginella species is caused by a physical effect, thin‐film interference. Predictions for a model film have been confirmed by electron microscopy of S. willdenowii and S. uncinata. For the latter species iridescence contributes to leaf absorption at wavelengths above 450 nm and develops in environments enriched with far‐red (730 nm) light. This evidence supports the involvement of phytochrome in the developmental control of iridescence.