Yellow Rattle

Yellow rattle is a herbaceous annual plant that resembles the larger greater yellow rattle (Rhinanthus angustifolius). The plant grows to up to 10–50 centimetres (4–20 in) tall, with opposite, simple leaves measuring 20–30 millimetres (0.8–1.2 in) × 5–8 millimetres (0.2–0.3 in). The leaves are sessile (they grow directly from the stem), somewhat heart-shaped at the base, otherwise ovate (oval-shaped) to lanceolate (shaped like a lance tip), dentate (toothed) and scabrid (a little rough to the touch). The stem, which stands upright, can be simple or branched, is four-angled and often streaked or spotted black. The yellow flowers are 13 to 15 millimetres (0.5 to 0.6 in) across and have a straight tube for the petals. The silvery-coloured fruit is a dry capsule, which contains loose, rattling seeds when ripe that give the plant one of its common names. The herbalist Nicholas Culpeper, in his The English Physician (first published in 1652), wrote of yellow rattle as being "good for cough, or dimness of sight". The plant has a reputation of being toxic to animals. The seeds contain iridoids which cause them to have a bitter taste.

Rhinanthus minor is found in Europe, western Russia, western Siberia, northern USA and throughout Canada. The preferred habitat of Rhinanthus minor is dry fields or meadows, where its flowering period is in the summer between May and September, but it can thrive with semi-natural species-rich water-meadows. It can tolerate a wide range of soil types but does not grow where the soil has a pH less than 5.0. Yellow rattle flowers are pollinated by bumblebees during the summer months; the plant is also capable of self-fertilization. Yellow rattle is an annual wildflower. It is hemiparasitic, in that it can gain its nutrients by penetrating the roots of neighbouring green plants with its own roots, but is a facultative parasite, in that it acts opportunistically when in contact with a root. The hemiparasitic nature of yellow rattle can result in stunted, unbranched individual specimens. The plant can associate with many different host species, notably Poaceae (grasses) and Fabaceae (legumes). In Ireland and Scotland, yellow rattle is often associated with Machair habitat, which consists of coastal grassland. The seeds are spread effectively by traditional hay-making practices. Farmers seek to remove it since it affects yields by weakening grass; it is an indicator of poor grassland.

Effects on plant community structure. …

Yellow rattle is used to proactively create or restore wildflower meadows. It is used to reduce the dominance of grasses, when more expensive methods, such as removing the nutrient-rich topsoil, or impractical methods, such as changing the timing and intensity of grazing, cannot be used. This improves the chances of other species of flowers becoming established. According to Natural England, the optimum density of yellow rattle plants needed to enable other species to be introduced is 100 to 200 per m2. Studies have shown that the plant's role in maintaining species diversity is through differential growth suppression effects and enhanced soil nutrient recycling. The yellow rattle seed is sown thinly onto grassland where gaps have been created, or where all the grass has been cut back and the clippings removed. Seeds can be also be introduced by the spreading of green hay. The grass should be kept short until the beginning of March, after which the seedlings become established. After the yellow rattle plants have germinated and matured, the fruits shed their seeds. The meadow hay is cut and removed to encourage the growth introduced wild flowers. The seed, which is short-lived, is sown in the autumn, using seed harvested that year. The seeds have to remain on or under the ground throughout the cold months of winter in order to germinate in the spring.