Wood cow-wheat[1] (Melampyrum nemorosum) is an herbaceous flowering plant in the family Orobanchaceae.

In Sweden it is called natt och dag (Night and Day).

[2] In Russia it is called Ivan-da-Marya (Ivan and Maria), a Christianisation of the traditional Slavic Kupalo-da-Mavka (Kupalo-and-Mavka).

The new leaves are blue, turning green as they mature.

This plant is a host to the rust fungus Coleosporium melampyri [3] und Cronartium flaccidum with the associated uredium and telium.