About Rhinanthus minor L.
Yellow rattle (Rhinanthus minor L.) is a herbaceous annual plant that resembles the larger related species greater yellow rattle (Rhinanthus angustifolius). It grows 10–50 centimetres (4–20 in) tall, with opposite, simple leaves that measure 20–30 millimetres (0.8–1.2 in) long by 5–8 millimetres (0.2–0.3 in) wide. The leaves are sessile, meaning they grow directly from the stem; they are somewhat heart-shaped at the base, and otherwise range from ovate (oval-shaped) to lanceolate (shaped like a lance tip). They are dentate (toothed) and scabrid (slightly rough to the touch). The upright stem can be simple or branched, is four-angled, and often marked with black streaks or spots. Its yellow flowers are 13 to 15 millimetres (0.5 to 0.6 in) across, and have a straight petal tube. The silvery-coloured fruit is a dry capsule; when ripe, it holds loose seeds that rattle inside, which gives the plant its common name. In 1652, herbalist Nicholas Culpeper wrote in *The English Physician* that yellow rattle was "good for cough, or dimness of sight". The plant has a long-held reputation for being toxic to animals. Its seeds contain iridoids that give them a bitter taste. Rhinanthus minor is distributed across Europe, western Russia, western Siberia, northern United States, and throughout Canada. It prefers dry fields or meadows, and can also thrive in semi-natural, species-rich water-meadows. It flowers in summer, between May and September. It tolerates a wide range of soil types, but will not grow in soil with a pH lower than 5.0. Its flowers are pollinated by bumblebees in summer, but the plant is also capable of self-fertilization. Yellow rattle is an annual wildflower that is hemiparasitic and facultative: it can obtain nutrients by penetrating the roots of neighboring green plants with its own roots, but only does so opportunistically when it comes into contact with a host root. This hemiparasitic nature can lead to stunted, unbranched individual plants. It can form associations with many different host species, most notably Poaceae (grasses) and Fabaceae (legumes). In Ireland and Scotland, it is often associated with Machair, a coastal grassland habitat. Traditional hay-making practices spread its seeds very effectively. Farmers typically aim to remove it, because it weakens grass and reduces hay yields, and it is considered an indicator of poor grassland. Yellow rattle is used to actively create or restore wildflower meadows. It is used to reduce the dominance of grasses in situations where more expensive methods like removing nutrient-rich topsoil, or impractical methods like changing the timing and intensity of grazing, cannot be used. Reducing grass dominance improves the chance that other wildflower species will successfully establish. According to Natural England, the optimum density of yellow rattle to support introduction of other species is 100 to 200 plants per m². Studies show that the plant maintains species diversity through differential growth suppression of other plants and enhanced recycling of soil nutrients. Yellow rattle seed is sown thinly onto grassland where gaps have been created, or where all existing grass has been cut back and clippings removed. Seeds can also be introduced by spreading green hay. Existing grass should be kept short until early March, after which yellow rattle seedlings become established. After yellow rattle plants germinate and mature, their fruits shed their seeds. The meadow hay is then cut and removed to encourage the growth of introduced wild flowers. The seed is short-lived, so it is sown in autumn, using seed harvested in that same year. The seeds must remain on or under the ground through the cold winter months to germinate the following spring.
