Its frequent habitat is the mountain forest, most often in clearings, up to 1,500 m in elevation (5,000 ft). In France, they live in the Alps, the Pyrenees and the Cévennes.
An annual herbaceous species, it is tall, about 20-60 cm (8-24 in). The stem is square in section, hairy on two opposite faces. The plant is indeed pubescent, i.e., covered by fine, tiny hair. Leaves are lanceolate, i.e., spearhead-shaped. Bottom leaves are whole whereas top leaves show a few long teeth at the base. They come in pairs, across the stem from one another. Bracts top the plant. They do so at their most decorative, their flashy purple color is worthy of a fashion show!
Flowers are likewise elegant, a bright yellow. They can be admired at the beginning of summer in June-July. The corolla is 16–20 mm (0.6–0.8 in.) long. It is fused, a curved tube in shape. Its upper lip is hooded and flat-sided; the lower lip has three lobes. In like manner to leaves, flowers grow in pairs.
Reproduction is ensured by pollination from butterflies whereas ants disseminate the seeds. During the fall season, the mature seeds are black and resemble wheat seeds.
Hence, the name of the plant from the Greek melos, black and puros, wheat. It is often attacked by the blister rust fungus Cronartium flaccidum.
According to Wikipedia, In Sweden it is called natt och dag. (Night and Day). In Russia it is called Ivan-da-Marya (Ivan and Maria), a Christianisation of the traditional Slavic Kupalo-da-Mavka.
I dedicate this leaf of an album to my brother Jean-Louis who presented me (August 2020) with a photograph of this plant taken in the Belledonne range of the French Prealps, near Allemont.