Species in the genus are variously native to Latin America, Australia, New Zealand, Papuasia, Hawaii, insular Southeast Asia, Africa, and Madagascar.

[5] The APG II system, of 2003, also recognizes this family and assigns it to the order Gunnerales in the clade core eudicots.

This represents a change from the APG system, of 1998, which firmly recognized two separate families, unplaced as to order.

The earliest fossilized pollen is known from the Late Cretaceous (Turonian) of Peru, about 90 million years ago, and within the following 10 million years, Gunnera had achieved a worldwide distribution, with fossil pollen grains being found in areas where it is not found today, such as western North America, mainland Australia, and Antarctica.

However, phylogenetic analysis indicates that the majority of Gunnera species, even those found on entirely different continents, diverged from each other during the Cenozoic, indicating that the modern distribution of Gunnera is a consequence of long-distance dispersal from South America to other parts of the world, rather than relics of a former cosmopolitan distribution.

The only species that diverged prior to the Cenozoic is Gunnera herteri, described from Uruguay[12] and distributed in Uruguay and southeastern Brazil, which is thought to be the most ancient species of the genus, its lineage having diverged during the Late Cretaceous, roughly concurrent with the oldest Gunnera fossil pollen from Peru.

The persistence of the Gunnera crown group since the Cretaceous makes it unique among flowering plants, and may have been facilitated by strong niche conservatism, dispersal ability, and being able to aggressively colonize disturbed land.

The giant rhubarb, or Campos des Loges (Gunnera manicata), native to the Serra do Mar mountains of southeastern Brazil, is perhaps the largest species, with reniform or sub-reniform leaves typically 1.5 to 2.0 meters (4 ft 11 in to 6 ft 7 in) long, not including the thick, succulent petiole which may be up to 2.5 meters (8 feet 2 inches) in length.

The width of the leaf blade is typically 2.5 meters (8 feet 2 inches), but on two occasions cultivated specimens (in Dorset, England in 2011[13] and at Narrowwater, Ulster, Ireland[14] in 1903) produced leaves fully 3.3 meters (10 feet 10 inches) in width.

For this reason, it has been suggested that Panke originates from South American Gunnera that colonized North America during the Cretaceous and grew into giant forms, with the remaining South American Gunnera evolving into the subgenus Misandra, with a low-lying, matlike growth.

During the Cenozoic, the North American Panke would have colonized Hawaii and retreated southwards on the mainland before recolonizing South America.

Gunnera perpensa is a source of traditional medicine in southern Africa, both in veterinary and human ailments, largely in obstetric and digestive complaints, but also as a wound dressing.