Parietaria is a genus of flowering plants in the family Urticaceae (the nettle family), order Rosales. It comprises annual and perennial herbaceous plants native to temperate and tropical regions worldwide, with greatest diversity around the Mediterranean basin.
Plants in the genus are typically small herbs reaching 20–80 cm in height, with green or pink stems. The leaves are alternate, simple, and entire, often bearing small clusters of leaves in their axils. Flowers are produced in axillary clusters and may be bisexual or unisexual (with staminate and carpellate flowers on the same plant); the fruit is a small, dry achene.
The genus is best known for Parietaria judaica (pellitory-of-the-wall), a Mediterranean species that has become widely naturalised across the Americas; conversely, the North American P. pensylvanica (Pennsylvania pellitory) has naturalised in parts of Europe. Several species are considered weeds. Parietaria pollen is a significant cause of allergic rhinitis in Mediterranean countries.
Distribution
Parietaria is native to temperate and tropical regions across the world, with the Mediterranean basin as a centre of diversity. The Mediterranean species P. judaica is widely naturalised in the Americas, while the North American P. pensylvanica is naturalised in parts of Europe; several species are regarded as weeds in their introduced ranges.
Ecology
Species of Parietaria frequently colonise walls, rocky ground, and disturbed habitats, which is reflected in the common name "pellitory-of-the-wall" for P. judaica. The genus is wind-pollinated; pollen from Mediterranean Parietaria species is a documented cause of allergic rhinitis and asthma in southern Europe.
Taxonomy Notes
Parietaria belongs to the family Urticaceae (order Rosales) and is one of several herbaceous genera in that family alongside Urtica and Pilea. As of November 2013, The Plant List accepted 10 species in the genus, though additional names remain unresolved. Several formerly placed species have been moved to other genera, including Freirea.
