Герань

Geranium oil does not come from the genus Geranium but from Pelargonium, a separate genus in the same family, Geraniaceae. Geranium flowers have five very similar petals and are radially symmetrical, whereas Pelargonium flowers have two upper petals that differ from the three lower petals, so they have a single plane of symmetry. Pelargonium graveolens is native to the Cape Provinces and the Northern Provinces of South Africa, Zimbabwe and Mozambique. The natural form of the plant smells of mint. Some cultivars have a scent similar to rose petals, while others have little or no scent.

Many plants cultivated under the species name Pelargonium graveolens are of hybrid origin and differ from wild specimens. Among the many cultivars grown under the name Pelargonium graveolens, the scents include rose, citrus, mint and cinnamon as well as various fruits. Nearly all Pelargonium cultivars grown for their rose-scented essential oil arose in Europe from crossings between introductions from South Africa and are of hybrid origin. The Rosat group of Pelargonium cultivars is a more or less erect, much-branched shrub, up to 1.4 m tall and strongly rose-scented. The common P. 'Graveolens', or P. 'Rosat', is cultivated on a large scale and its foliage is distilled for its scent. Pelargonium distillates and absolutes, commonly known as "geranium oil", are sold for aromatherapy and massage therapy applications. Geranium oil is sometimes adulterated with synthetic citronellol and geraniol. The flowers and leaves of the plant are also used as a flavoring in cakes, jams, jellies, ice creams, sorbets, salads, sugars and teas.

The main chemical components of geranium oil from Réunion are geraniol, citronellol, isomenthone, geranyl formate, citronellyl formate, linalool, guaia-6,9-diene and cis-rose-oxide. Although the proportions of the compounds may vary and oils from different origins can be distinguished by their odour, geranium oils are quite uniform in composition. Analyses of Indian geranium oils showed that the major constituents, in terms of percentage composition, were citronellol + nerol and geraniol. The sesquiterpene 10-epi-γ-eudesmol is found in oils from Africa and Egypt, whereas guaia-6,9-diene is prominent in oils from Reunion (Bourbon) and China. Citronellol is a natural acyclic monoterpenoid. The (-)-enantiomer of citronellol is widespread, but particularly abundant in the oils of rose and Pelargonium geraniums. Geraniol is a monoterpenoid and an alcohol, and a primary component of rose oil. Rose oxide is a fragrance chemical found in roses and rose oil. It also contributes to the flavor of some fruits, such as lychee, and wines, such as Gewürztraminer. Of the rose oxide isomers, only the (-)-cis isomer, with an odor threshold of 0.5 ppb, is responsible for the typical rose (floral green) fragrance.

For optimum growth the Rosat group requires an average annual rainfall of 1000-1500 mm. A 3-month dry period improves herbage yield and oil content. Oil produced after a 3-month wet period had a slightly milder note and an increased geraniol content. The plants require much light, and cloudy weather reduces leaf growth and oil content. An average daytime temperature of 20-25°C is optimal. Growth stops at 6°C; frost and even prolonged exposure to 3°C kills the plants. In termperate areas, the Rosat group is therefore grown as an annual crop. The Rosat group is propagated vegetatively, mostly by stem cuttings. To plant 1 ha, 30 000-50 000 cuttings are needed.