Selaginella willdenowii is a species of spikemoss known by the common names Willdenow's spikemoss and peacock fern due to its iridescent blue leaves. Like other Selaginallales, it is fern ally and not a true fern.

The blue iridescence is produced by thin-film interference produced by a thin layer of cells with lamellar structure in the upper cuticle of leaves. It is suggested that this adaptation reduces the effect of strong sun beams filtering through the canopy that would otherwise damage shade-adapted species. Blue iridescence is found also Selaginella uncinata and both species are adapted for extreme shade below the forest canopy.

Selaginella willdenowii is sometimes listed as Selaginella willdenovii.