Sainfoins (Onobrychis) are Eurasian perennial herbs that have pale pink flowers and round single-seeded pods (see image below). O. viciifolia is naturalized throughout many countries in Europe and North America grasslands on calcareous soils. The Flora Europaea lists 23 species of Onobrychis.
This highly nutritious plant was an important forage for heavy working horses in agriculture and a good source of nectar for honey bees in Britain. Because the plant is rich in tannins which protect proteins from hydrolysis in the rumen, the proteins are instead absorbed in the abomasum. The plant has a deep taproot and so is very drought-resistant, but does not recover well from grazing. Sainfoin is difficult to establish, only yields one crop per year and is not persistent in grassland so is seldom grown in any significant acreage.
A species, Onobrychis caput-galli, is known as the "Cock's Head" in English (cf. Latin caput galli).
Sainfoin comes from French sain foin: sane hay.
XVIe s.— L'herbe appellée en France sain-foin, en Italie herba medica, en Provence et Languedoc luzerne. De l'excessive louange qu'on a donné à ceste plante, à cause de sa vertu medecinale et engraissante le bestail qui s'en paist, vient ce mot de sain (O. de Serres)
Onobrychis comes from Greek onos (ass) and brycho (to eat greedily), referring to its properties as a forage plant.