- Name also: Yellow-rattle, Cockscomb, Little Yellow Rattle
- Family: Broomrape Family – Orobanchaceae
(formerly Figwort Family – Scrophulariaceae)
- Growing form: Annual herb, hemiparasite.
- Height: 20–40 cm (8–16 in.). Stem branchless or sparely branched, brownish green, usually without markings.
- Flower: Corolla zygomorphic, 13–15 mm (0.52–0.6 in.) long, dark yellow, fused, bilabiate, with long, straight tube. Upper lip hooked, flat-sided, tip with 2 short, blunt, purple teeth. Lower lip 3-lobed. Calyx 4-lobed, oval, wide, dark. Stamens 4. Gynoecium fused, single-styled, body inside corolla’s upper lip. Flowers borne in short spike-like clusters, terminating stem and branches.
- Leaves: Opposite, stalkless. Blade narrowly ovate–narrowly elliptic, with shallow, blunt-toothed margin. Central leaves usually with max. 10 pairs of veins. Subtending bracts ovate, brownish green.
- Fruit: Brown, flat, approx. 7 mm (0.28 in.) long capsule inside calyx.
- Habitat: Road and field banks, meadows, sloping meadows, pastures.
- Flowering time: June–July.
Yellow rattle is a hemiparasite: it sucks nutrition from its neighbour’s roots, although it can also assimilate itself. Its host plant can be one of over fifty species – apparently any old meadow plant will do. Its favoured targets are however legumes because of their high levels of nitrogen.
Two species of yellow rattles grow in Finland, yellow rattle and narrow-leaved rattle (R. serotinus). Yellow rattle can be further divided into two subspecies, which are also regarded as their own species: ssp. minor and ssp. groenlandicus grow all over Finland and, although they are very similar, they can be distinguished on the basis of their leaves. The leaf blades on ssp. minor are thin and shallow-toothed, while on ssp. groenlandicus they are uniformly thick and large-toothed. There are also small differences regarding the construction of the flower and especially in the calyx. Ssp. minor arrived in Finland in ancient times and is found in meadows, pasture land and on banks. Ssp. groenlandicus is native to a small area in the northwest fell region where it grows beside streams. It has since travelled south along with people to at least Sodankylä and Kittilä. In the southern part of its habitat it meets ssp. minor, and they cross-breed to produce hybrids.
Yellow rattle can be differentiated from its relative narrow-leaved rattle on the basis of its flowers. Narrow-leaved rattle’s calyx-tube curves upwards, the whole flower and especially the teeth on the upper labellum of the calyx are larger, and the body of the pistil separates from the upper labellum.