Rhinanthus angustifolius, the narrow-leaved rattle or greater yellow-rattle, is an annual wildflower native to temperate grasslands in much of Europe, and north and central Western Asia. The yellow flowers are mostly visited by bumblebees.
Greater yellow rattle grows 20 to 60 cm tall. It has opposite, simple leaves, with a serrated margin. The yellow flowers are two lipped, with purple teeth on the upper lip. Behind the flower the joined sepals form a green bladder [the calyx]. The calyx turns brown in fruit and holds the rounded capsule in which the seeds rattle about, hence its common name.
As a hemiparasite, greater yellow rattle sucks nutrition from its neighbor’s roots. At the same time, it performs in its green leaves photosynthesis and transforms carbon dioxide and water into sugars.