Lavatera arborea or Malva dendromorpha, the Tree Mallow, is a species of mallow native to the coasts of western Europe and the Mediterranean region, from the British Isles south to Algeria and Libya, and east to Greece.
It is a shrubby annual, biennial or perennial plant growing to 0.5–2 m (rarely 3 m) tall. The leaves are orbicular, 8–18 cm diameter, palmately lobed with five to nine lobes, and a coarsely serrated margin. The flowers are 3–4 cm diameter, dark pink to purple and grow in fasciculate axillary clusters of two to seven. It grows mainly on exposed coastal locations, often on small islands, only rarely any distance inland.
Although long considered a species of Lavatera, genetic and morphological analysis by Martin Forbes Ray, reported in 1998, suggested it was better placed in the genus Malva, in which it was named Malva dendromorpha M.F.Ray.
Tree Mallow was considered a nutritive animal food in Britain in the 19th century, and is still sometimes used as animal fodder in Europe.
Lavatera arborea has long been cultivated in British gardens, as described in the 1835 self-published book British Phaenogamous Botany, which used the then-common name Sea Tree-mallow: "This species is frequently met with in gardens, where, if it is allowed to scatter its seeds, it will spring up for many successive years, and often attain a large size. The young plants will, as Sir J. E. Smith observes, now and then survive one or more mild Winters; but having once blossomed it perishes."
While sometimes detrimental to seabird habitat, management of Tree Mallow (both planting and thinning) has been successfully employed to shelter nesting sites of the threatened Roseate Tern, which requires more coverage than Common Terns to impede predation.
The Tree Mallow's recent increased range among Scottish islands has raised concerns that it is displacing native vegetation, and is reducing Atlantic Puffin (Fratercula arctica) populations in affected areas. The plant forms dense stands along the island coasts that inhibit breeding, and causes the puffins to abandon their burrows.
Its spread among Australian islands in recent decades is thought to be reducing biodiversity, soil retention, and seabird habitat. According to one study, "Crested and Caspian Terns that nest in the open are closed out by the canopy, and Little Penguins (Eudyptula minor) and Bridled Terns (Sterna anaethetus) are excluded by the lack of undergrowth".