The Fern (Horisme tersata) is a Palearctic moth of the Geometridae family, found in open woodlands, hedgerows, and grasslands. It is most common in parts of Europe, where its caterpillars feed on Traveller's-joy (Clematis vitalba). The adult moth is known for its subtle, indistinct markings, which can make it hard to distinguish from the closely related Cryptic Fern (Horisme radicaria).