Erva TostãoBoerhavia diffusa

Did you know?

• Punarnava means "new again" in Sanskrit. The old rootstock lies dormant through the hot, dry season and sprouts afresh when the rains return^{[5, 6, 8]}.

• The genus is named for Herman Boerhaave (1668–1738), a Dutch physician and professor of botany. It is often misspelled Boerhaavia, including on some of our own labels^{[3, 5, 11]}.

• Erva tostão belongs to the four-o'clock family, alongside bougainvillea and the garden four-o'clock, Mirabilis jalapa^{[5, 10, 12]}.

• Its small, ribbed fruits are covered in sticky glandular hairs and cling to whatever brushes past, which is how the seeds travel^{[4, 6, 7]}. Two of its Brazilian names, pega-pinto and agarra-pinto, are built from Portuguese words for "grab" and "chick"^{[3, 4, 9]}.

• It is quick off the mark: a seedling can flower about four weeks after sprouting, and with enough water it flowers and fruits all year^{[4, 7]}.

• The leaves are cooked and eaten as a green vegetable, in sauces in West and East Africa and in curries and soups in India, and the seeds are sometimes added to cereals, for example in Senegal and Mali^{[4, 5, 6, 7]}.

Origins and history

Erva tostão is an annual or perennial herb with fleshy stems that spread along the ground and then turn upward, reaching about 1 to 2 meters (3 to 6 feet)^{[4, 5, 7]}. It grows from a long, thick, fleshy taproot^{[4, 7]}, and its tiny flowers range from pink to purplish red^{[4, 5, 6]}. It thrives in sun on open, disturbed ground: roadsides, field edges and the margins of towns^{[3, 4, 5, 7]}.

Carl Linnaeus described Boerhavia diffusa in his Species Plantarum in 1753^{[1, 2]}. The genus honors Herman Boerhaave, the Dutch physician who was also professor of botany at the University of Leiden^{[5, 11]}. The plant itself is harder to pin down. It now grows across the tropics of Africa, Asia, the Americas and the Pacific, and its original home is uncertain; one authority suggests the Old World tropics^{[4, 7]}. Kew counts it as native across much of Brazil and in Peru, while Brazil's official flora records it as naturalized in Brazil^{[1, 3]}. Botanists also differ over how widely to draw the species, and some fold close relatives such as B. coccinea and B. repens into it^{[1, 4]}.

In India the plant is punarnava, used in Ayurveda as a rasayana, a herb for renewal^{[6, 8]}. The root, leaves and seeds are all used^{[4, 5, 8]}. It is also a food plant: its leaves are cooked as a leafy green in India and Africa, and they supply vitamin C and calcium^{[4, 5, 6]}. In central Australia, Aboriginal people have eaten its long, fleshy root^[7]. In Brazil it is also called simply tostão, the name of an old Portuguese coin worth 100 réis^[9], and erva-de-porco, "pig's herb," which echoes the English hogweed^{[4, 13]}.

Traditional uses

Clinical studies of erva tostão in people are still few, but its traditional use is rich, stretching from Ayurveda in India to Africa and the Americas^{[4, 5, 6, 13]}.

• A renewing tonic

  In Ayurveda punarnava is valued as a rasayana, a herb for renewal. It supports energy and vitality.*^{[6, 8]}

• Kidney function

  The root has long been used in India and Africa to support the kidneys. Erva tostão supports healthy kidney function and normal urinary flow.*^{[4, 5, 6, 8]}

• Liver function

  Traditionally valued for the liver in Ayurveda and beyond, erva tostão supports healthy liver function.*^{[5, 6, 8]}

• Bile flow and digestion in South America

  In Brazil the whole plant, and especially the root, is a traditional herb for digestion and the liver, and in Argentina the root is taken to support the flow of bile. Erva tostão supports healthy bile flow and digestion.*^[13]

• A leafy green

  The leaves are cooked as a vegetable in sauces, soups and curries.^{[4, 6]}

Plant compounds

Erva tostão contains a distinctive group of plant compounds called rotenoids, the boeravinones^{[4, 5, 6]}. It also contains the alkaloid punarnavine, together with punarnavoside, ursolic acid and beta-sitosterol^{[4, 5, 6, 8]}. The leaves contain the flavonoid quercetin, and they provide vitamin C and calcium^{[5, 6]}.