Primulaceae

Low herbs of northern temperate meadows, woodland and mountains, typically with a basal rosette of leaves and five-petalled flowers on a leafless stalk. The medicinal member here is primrose root (Primula veris, and often P. elatior with it), one of the classic European expectorants.

Its triterpene saponins are concentrated in the root and work indirectly: they irritate the gastric mucosa, and that irritation triggers a reflex increase in bronchial secretion through the vagus nerve. It is the same mechanism that puts senega and ivy in the same group, and the same mechanism that sets the dose ceiling, since pushing it produces nausea. The family name is a persistent source of confusion with evening primrose, an unrelated plant in the Onagraceae.