The stevia plant
Stevia rebaudiana Bertoni is a small, shrubby plant and belongs to the family of composite flowers (Asteraceae or Compositae). The Stevia plant is native to Paraguay and prefers sandy soils near water. In the wild, the stevia plant can reach a height of up to 75cm.
Stevia rebaudiana Bertoni is the Latin name of the stevia plant. It is composed of the generic name Stevia, the species name rebaudiana and the subspecies name Bertoni. There are over 150 other Stevia plant species, of which only the Stevia rebaudiana species contain the sweet steviol glycosides. This Stevia plant species is therefore also known as honey leaf, honeywort, sweet herb by the indigenous population, the Guarani and Mato Grosso Indians in Paraguay and Brazil. In the Guarani language in Paraguay, the sweet herb is also called caá jeé, kaá heé, or yerba dulce.
The botanist Moisés Bertoni was the first to discover the sweet ingredients of the stevia plant. The individual components of the Stevia leaves, the steviosides, the rebaudiosides A to F were analysed and broken down by the chemist Ovidio Rebaudi.
The origin and distribution of Stevia
The highlands of Argentina, Brazil and Paraguay from the 22nd to 23rd southern latitude and from the 55th to 56th western longitude are the natural home of the stevia plant. The soil conditions and the moderately humid climate in the border region between Argentina, Brazil and Paraguay, with an average annual temperature of 21°C and annual precipitation of 1500 to 1800 mm, form an ideal distribution area for the Stevia rebaudiana plant genus. On the sandy, acidic and clayey plateaus of the Amambai, in the state of Mato Grosso do Sul on the border between Brazil and Paraguay, the sweet stevia species grow particularly well.
Today, the stevia plant is cultivated in Latin America, South-East Asia and almost all continents of the world to extract the sweet components, the steviol glycosides and rebaudiosides. The sweeteners are obtained in a complex extraction process.
The Stevia Botany
The Stevia rebaudiana plant is a shrubby plant and belongs to the composite family (Asteraceae or Compositae). The Stevia plant is native to Paraguay and prefers sandy soils. In a frost-free climate, the Stevia plant develops a strong rootstock from which perennial Stevia shoots grow up to one meter high. The Stevia plant belongs to the flat-root family, which means that the Stevia roots spread out in a plate-like manner in the upper soil layers.
The Stevia leaf
The stems of the stevia plant develop into lancet leaves, sickle-like, pointed, serrated leaves. The light to dark green, up to 8 centimetre long Stevia leaves are arranged opposite each other and have plant hairs on the leaf surface. Depending on the Stevia plant species, the Stevia leaf shapes can be ovoid or diamond-shaped.
The ingredients of dried Stevia rebaudiana leaves
In the leaves of Stevia rebaudiana the sweet-tasting components, the steviol glycosides or steviosides, are formed. These give the Stevia plant its sweetness. The most important are the steviol glycosides and rebaudioside A. Other sweeteners such as dulcoside A, rebaudioside B, C, D, E, F and steviolbioside are also found in the Stevia leaves of the plant. Based on the dry weight of the Stevia leaves, a Stevia leaf contains 5-10% stevioside, 2-4% Rebaudioside A, 1-2% Rebaudioside C and 0.4-0.7% dulcoside A. Dried Stevia leaves are 20 to 30 times sweeter than sugar and the extract obtained from it, steviol glycosides up to 300 times sweeter.
Other ingredients of Stevia leaves
Stevia rebaudiana leaves are a good source of proteins and carbohydrates. The content of inorganic minerals is attributed to the high ash content. The minerals and secondary plant substances contained in Stevia leaves are also important.
The Stevia Blossom
The Stevia flowers are arranged in an irregular inflorescence and are about 7-15 mm large. The capitula of Stevia rebaudiana are terminal and grouped together to form cyme-shaped umbels. These consist of white 5-flowered cylindrical flower heads. A Stevia rebadiana shoot can have between 10 and 200 flower heads. The fruit of the Stevia plant is thin and long and has 4 to 5 edges.
A characteristic of Stevia flowers is self-sterility (self-infertility). This is the name given to plants that are unable to fertilise themselves. After pollination with pollen of its own genus (genotype) the seeds are not formed. The wind does this under natural conditions by carrying the pollen of the Stevia flowers from Stevia plant to Stevia plant, and this is the only way to produce seeds. This type of sexual reproduction is also called wind pollination and is also found in apple, pear and sweet cherry varieties.
The formation of Stevia seeds
The Stevia seed is about 3 mm long and belongs to the family of the solitary indehiscent fruit (achenes, like dandelions). The seed of the Stevia plant has a feather-like crown of hair that can fly. After the ripening process, the Stevia seeds, which form in seed corollas, fall out easily. Stevia is a light germinator and on moist soil the germination time is 14 days at a germination temperature of 20-25 degrees.
The Stevia seed is known for its low germination rate of 12 to 15 percent, even with optimal seed. Another much simpler method is the vegetative propagation of the Stevia plant using cuttings. Today, many nurseries and garden centres can buy a Stevia plant and keep it in the garden in summer.
The vegetative propagation and cultivation of Stevia
Vegetative propagation of the Stevia plant via cuttings is much easier than germinating Stevia seeds.