These are very commonly grown flowers in farmer’s fields.
Oenothera. What’s interesting is it has flowers of two colours on the same stalk. See closeup below.
Oenothera is a genus of about 125 species of annual, biennial and perennial herbaceous flowering plants, native to North and South America. Origins are thought to be Mexico and Central America but they are quite naturalized in Japan.
During the Pleistocene era a succession of ice ages swept down across North America, with intervening warm periods. This was repeated for four ice ages, with four separate waves of colonization, each hybridizing with the remnants of the previous waves. This generated a present-day population that is very rich in genetic diversity, spread right across the North American continent.
It is the genus of the family Onagraceae. Onagra (meaning “(food of) onager”) was first used in botany in 1587.
Its modern name Oenothera was published by Carolus Linnaeus in his Systerma Naturae, also has a donkey-related origin, meaning “ass-catcher”. In Greek oeno means “donkey”, while thera means “to catch, trap, pursue”. It is believed that the name refers to the toxicity of the plant that can be used to trap donkeys and other animals.
Common names include evening primrose, suncups, and sundrops.
The species vary in size from small alpine plants 10 cm tall, to vigorous lowland species growing to 3 m. The leaves form a basal rosette at ground level and spiral up to the flowering stems; the leaves are dentate or deeply lobed (pinnatifid). The flowers open in the evening, hence the name “evening primrose”, and are yellow in most species but white, purple, pink or red in a few; there are four petals. One of the most distinctive features of the flower is the stigma with four branches, forming an X shape. Pollinated by moths and bees, however, the pollen grains are loosely held together by viscin threads (see photo below), meaning that only bees that are morphologically specialized to gather this pollen can effectively pollinate the flowers (it cannot be held effectively in a typical bee scopa). Furthermore, the flowers are open at a time when most bee species are inactive, so the bees which visit Oenothera are also compelled to be vespertine temporal specialists. The seeds ripen from late summer to fall.
In the wild, evening primroses acts as primary colonizers, springing up wherever a patch of bare, undisturbed ground may be found. This means that they tend to be found in poorer environments such as dunes, roadsides, railway embankments and wasteland. It often occurs as a casual, eventually being out-competed by other species.