Cultivar-group name proposed in PROSEA 19: Essential-oil plants (1999).
2n = 77 (heptaploid)
Pelargonium asperum auct. non Ehrh. ex Willd., Pelargonium graveolens auct. non L'Hér., Pelargonium roseum auct. non Ehrh.
Rose-scented pelargonium, Bourbon geranium (En). Géranium rosat (Fr).
Origin and geographic distribution
Pelargonium comprises about 260 species, most originating from coastal South Africa from Namaqualand to Port Elizabeth. Many Pelargonium species are so easy to grow and have become so popular as garden plants that they are now cultivated worldwide.
Nearly all cultivars of Pelargonium grown for their rose-scented essential oil, called geranium oil, arose in Europe from crossings between introductions from South Africa and are therefore of hybrid origin. Commercial cultivation began in the early 19th Century in Grasse, France. Grasse remained the main centre of production until the Second World War. As a result of a change in the economic climate, cultivation there has ceased. The production of Pelargonium Rosat Group became important in Algeria, Morocco and Réunion, using plants from Grasse, but after increasing steadily for some time, production declined. The most important producers of geranium oil are currently China, Egypt, Morocco and Réunion, but extensive industries of local importance exist in India and the Crimea Peninsula, the Caucasus and Tajikistan.
In Kenya independent introductions of Pelargonium from South Africa (or possibly via India) led to the development of the ‘Mawah oil’ industry in the early 20th Century. The industry all but ceased during the Second World War. After the war a new industry was built up using plant material from Réunion. The odour of the oil produced was intermediate between the original Mawah oil and Réunion geranium oil. Production of this oil virtually stopped after Kenya gained independence in 1963.
Pelargonium Rosat Group is grown for the essential oil obtained from the leafy parts. This rose-scented oil is one of the most widely used fragrance materials and an essential component of most rose-scented perfumes and soaps. Extracts of the leaves of Pelargonium Rosat Group have antifeedant properties against slugs. In India, the essential oil has shown nematicidal activity against Meloidogyne incognita. In Singapore, Malay women sometimes hide a fragrant Pelargonium leaf in their hair.
Production and international trade
The main producer of geranium oil in the past was Réunion and its oil still sets the standard against which oils from other origins are valued. China is now the main producer. Other major producers are Egypt, Morocco, Réunion, India and the former Soviet Union. Annual world production is about 300 t, while demand is estimated at 500 t. The main importers are the United States, Europe and Japan. The production from India and the former Soviet Union is used entirely locally. Pelargonium Rosat Group is commonly grown by smallholders. It is often intercropped, e.g. in fruit orchards or with pulses. Investments for mechanization and distillation become profitable for plantations of 200–300 ha.
Geranium oil freshly steam-distilled from the herbage of Pelargonium Rosat Group is a pale green, mobile liquid with an unpleasant top note partly due to the presence of dimethyl-sulphide. This note disappears on proper aeration or ageing of the oil. When the oil ages, the green colour fades, the oil becomes more yellow and its odour acquires a green leafy-rosy body with minty notes and a sweet-rosy herbaceous dry-out lasting about 5 days. The fragrance compounds are stable under slightly alkaline conditions, e.g. in soap. Geranium oil is only occasionally used as a flavouring material because of its bitter taste.
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.
‘Rhodinol ex Geranium’ and ‘Terpeneless Geranium oil’ are selected fractions of vacuum-distilled geranium oil. In this distillation process the monoterpenes and several other low-boiling components are removed as are usually also the ‘tail’ fractions of the distillation. The odour of terpeneless geranium oil varies according to the supplier. Rhodinol ex Geranium has a delightfully sweet, fresh, rosy, uniform and tenacious aroma, and is used extensively in perfumery.
In Morocco, herbage of Pelargonium Rosat Group is often extracted with petroleum-ether to yield geranium concrete, which can be subsequently distilled to produce geranium absolute. The concrete is a dark-green or brownish-green waxy substance with an intensely earthy-herbaceous, somewhat sharp rosy odour with a note of green foliage and is of great tenacity. It is used in expensive soap perfumes. The absolute is a green or dark green liquid with an intense and very powerful odour. The leafy-green top notes are quite pronounced, but the body and dry-out are characterized by rich rosy notes with a minty undertone. The odour is less sharp and more tenacious than that of the steam-distilled oil. The absolute is used in high-class rose bases that are used in a wide variety of perfumes.
Geranium oil has been approved for food use by the Food and Drug Administration (FDA) of the United States under paragraph 182.20. The oil has been ‘generally recognized as safe’ in the United States (GRAS No 2508) and is registered by the Council of Europe under number 324n. Geranium oil is used in food products, including alcoholic and non-alcoholic beverages. Concentrations are below 0.001% (10 ppm) in finished products.
Adulterations and substitutes
Geranium oil is sometimes adulterated with synthetic citronellol and geraniol.
More or less erect, much-branched shrub, up to 1.4 m tall and 1 m in crown diameter, strongly rose-scented, with an extensive, spreading, superficial root system seldom penetrating below 30 cm; stem soft, grey-green, hairy, becoming darker and woody with age. Leaves opposite or alternate, soft, fragrant, hirsute with glandular and non-glandular hairs; stipules asymmetrically triangular, about 6 mm × 4 mm; petiole up to 3 cm long; blade ovate in outline, about 7 cm × 5 cm, 5–7-palmatifid to palmatisect, base cordate, apex obtuse, margins somewhat revolute. Inflorescence terminal, head-like, with 5–10 flowers in a small compact pseudo-umbel; peduncle up to 6 cm long. Flowers zygomorphic, 5-merous, rose-violet; receptacle forming a hypanthium with a nectariferous spur opening at base of the posterior sepal, lower end of spur thickened and with a nectariferous gland; sepals lanceolate, imbricate, unequal, connate at base, green-brown; petals free, spatulate, 2 posterior larger than the 3 anterior ones; stamens 10, connate at base, staminodial; ovary superior, 5-lobed, style filiform, stigma with 5 recurved, thin branches. Fruit not formed.
Other botanical information
Most Pelargonium species occur in South Africa, several are known from eastern Africa, 2 from Turkey and Iraq, and several occur in south-eastern Australia and Tasmania, some of which may have been introduced from South Africa or developed from such introductions, but most of which were hypothesized to reflect a single late-Pliocene dispersal event, based on DNA sequence. Pelargoniums are commonly called geraniums in commerce and by users. However, botanically, the genus Geranium is different from the genus Pelargonium. Geranium species (about 400) have regular flowers with 10 fertile stamens and without a nectar spur; Pelargonium species (about 260) have irregular flowers with usually only 2–7 fertile stamens and a nectar spur adnate to the pedicel.
Many Pelargonium species contain essential oil but none of the wild species are directly involved in commercial oil production. Three wild species are indirectly involved in the development of commercial essential-oil cultivars, mainly by hybridization and subsequent vegetative propagation:
– Pelargonium capitatum (L.) L'Hér.: 2n = 66 (hexaploid). Decumbent, much-branched, rose-scented subshrub up to 1 m tall, with crisped, villous, 3–5-lobed or -partite leaf blades, flowers pale pink to pink-purple in a 8–20-flowered head-like pseudo-umbel and with pedicel much shorter than the hypanthium. It grows wild along most of the south coast of South Africa on sandy dunes or flats.
– Pelargonium graveolens L'Hér.: 2n = 88 (octoploid). Synonym: Pelargonium asperum Ehrh. ex Willd. Erect, much-branched, strongly rose-scented shrub, up to 1.3 m tall, with palmatipartite to pinnatisect leaf blades soft to the touch (villous) and with irregularly pinnatipartite to pinnatisect segments, flowers white to pinkish-purple in a 3–7-flowered pseudo-umbel, pedicel usually shorter than hypanthium. It grows wild in mountainous areas in southern Africa, and is recorded from Zimbabwe, Mozambique and South Africa (northern Transvaal and south-eastern Cape Province).
– Pelargonium radens H.E.Moore: 2n = 88 (octoploid). Synonym: Pelargonium radula (Cav.) L'Hér. An erect, much-branched, rose-scented shrub, up to 1.5 m tall, with palmatisect to pinnatisect leaf blades with narrow, pinnatisect, scabrous segments, flowers pinkish-purple in a 3–8-flowered pseudo-umbel and pedicel as long as hypanthium. It grows wild in coastal regions of the southern Cape Province of South Africa, often in mountainous, rather moist habitats. Pelargonium Rosat Group consists of those cultivars yielding commercial rose-scented geranium oil. This group originates from the cultivars that have long been grown in Grasse (France) and which have been distributed from there to all major production areas. It is not clear, however, to what extent later independent introductions have contributed to the complex of hybrids. The typical and commercially most important cultivar in Réunion is ‘Rosé’, a hybrid between Pelargonium capitatum and Pelargonium radens. Other cultivars may be hybrids of Pelargonium capitatum and Pelargonium graveolens. Most of these cultivars have 77 chromosomes, and their morphology and essential oil yield are also in between their natural parents. However, the oil composition depends on the Pelargonium capitatum parent, which transmits the ability to synthesize geraniol and citronellol rather than isomenthone. Furthermore, the presence of guaia-6,9-diene is also inherited from Pelargonium capitatum. Réunion type cultivars are typical of Pelargonium Rosat Group. Future research should more clearly demarcate the cultivar-group.
Before the Réunion Rosat Group cultivars were proven to be hybrids of Pelargonium capitatum and Pelargonium radens, the pelargoniums grown for their essential oil were often called Pelargonium graveolens, Pelargonium roseum or Pelargonium asperum in the botanical literature, with scant regard for botanical accuracy. The name Pelargonium roseum has been applied by various authors to 3 different hybrid combinations (one of which possibly includes Rosat Group cultivars but is not the oldest one and should be rejected). Pelargonium ×asperum was proposed by H.E.Moore as the correct name for the hybrid of Pelargonium graveolens and Pelargonium radens. As Pelargonium graveolens is not involved in the origin of typical Rosat Group cultivars, Pelargonium graveolens and Pelargonium ×asperum are not acceptable as correct names. Moreover, a cultivar classification is more appropriate for cultivated plants; hence Pelargonium Rosat Group is preferred.
‘Scented-leaved Pelargoniums’ are a different group of cultivars grown as ornamentals. This group contains cultivars with a wide range of habits and foliage, often with numerous small flowers and characterized by their fragrance. Their scent varies and may be apple, peach, orange, lemon, nutmeg, peppermint, balsam or rose. ‘Attar of Roses’ and ‘Clorinda’ (rose-scented), ‘Chocolate Peppermint’ and ‘Joy Lucille’ (peppermint-scented), ‘Mabel Grey’ and ‘Lady Mary’ (lemon-scented), ‘Peach Cream’ (peach-scented), ‘Prince of Orange’ (orange-scented) and ‘Viscosissimum’ (balsam-scented) are some well known cultivars. Their relation to wild species with fragrant leaves should be further investigated, e.g. the relation to Pelargonium crispum (Bergius) L'Hér. (lemon-scented), Pelargonium fragrans Willd. (nutmeg-scented), Pelargonium odoratissimum (L.) L'Hér. (apple-scented) and Pelargonium tomentosum Jacq. (peppermint-scented).
Although the essential oils extracted from Pelargonium are called geranium oil in commerce, only one true Geranium species is grown commercially for its essential oil: Geranium macrorrhizum L., yielding zdravetz oil. All zdravetz oil is produced in managed natural stands in Bulgaria, the former Yugoslavia and former Soviet Union.
Growth and development
Oil content of Pelargonium Rosat Group changes during development. In Israel, it was found to be 1.2 g per 100 g dry matter at the beginning of flowering, gradually increasing to 1.3% at full bloom and dropping to 1.2% one week later and to 0.6% at the end of blooming. At full bloom, oil content was found to be highest in the flowers (3.3%), followed by the leaves (1.8%). Stems contained only traces of oil.
Main flowering periods in Réunion are April–May and August–September.
For optimum growth Pelargonium Rosat Group requires an average annual rainfall of 1000–1500 mm. Rainfall may be evenly distributed, but a 3-month dry period improves herbage yield and oil content. Oil produced after a 3-month wet period, however, had a slightly milder note and an increased geraniol content. Heavy rainfall combined with mist or fog may lead to root and stem rot. The plants require much light; cloudy weather reduces leaf growth and oil content. An average daytime temperature of 20–25°C is optimal, but growth is acceptable from 15–30°C and absolute maximum temperatures of 42°C for several weeks are tolerated in Hyderabad, India. Growth stops at 6°C; frost and even prolonged exposure to 3°C kills the plants. In temperate areas, it is therefore grown as an annual crop. In Réunion Pelargonium Rosat Group can be grown up to 1400 m altitude, but from sea-level to 400 m altitude other crops are more profitable. In the highlands of Kenya it is grown at 2000–2500 m altitude, in southern India at 1200–1500 m. Altitude and temperature have a pronounced influence on the character of the oil. In a trial in India herbage and oil yields at 900 m altitude were higher than at 550 m and at 2200 m. At the lower altitudes the essential oil was richer in isomenthone and citronellyl formate, at higher altitudes in menthone, citronellol and geraniol. At the lowest altitude the content of rose oxides was significantly higher than at the other altitudes. High maximum temperatures reduce oil content, but increase the content of citronellol and citronellyl formate. In Réunion cyclones often cause havoc in Pelargonium fields; soils saturated by prolonged heavy rains associated with cyclones also cause extensive damage.
Pelargonium Rosat Group grows best on fertile, well-drained, slightly sandy soils with pH 5.5–8.0. Heavy clays, alkaline and very acid soils are generally unsuitable. Waterlogging is not tolerated. Selected cultivars can tolerate low to moderate salinity.
Propagation and planting
Pelargonium Rosat Group is propagated vegetatively, mostly by stem cuttings. Micropropagation methods have given excellent results, but are more expensive. Leafy stem cuttings of 15–20 cm length with 4–6 nodes and a terminal bud are taken from healthy plants. Some 20–25 cuttings can be taken from a vigorous plant. Direct planting is common and striking rates are high when planted in moist soil, but nursery planting is also used. Before the cuttings are planted the lower leaves are removed and the base of the stem is cut at an angle and dipped in a fungicide. Cuttings should be planted immediately after preparation. 30,000–50,000 cuttings are needed to plant 1 ha. Equipment for mechanized planting is available, but manual planting is common. Prior to planting careful soil cultivation and removal of weeds and crop residues are essential, as Pelargonium Rosat Group is very susceptible to root infections and weeds are difficult to remove from an established crop.
Regular weeding of Pelargonium Rosat Group is needed until the crop is established. Care is needed to avoid damage to the shallow root system. Herbicides have been used successfully and should be applied as directed sprays with drift shields. For small farmers, who do most weeding manually, spot spraying against persistent weeds is recommended.
Nutrient uptake is high, but amounts reported vary greatly. In Réunion a crop of 7 t/ha fresh herbage removes an estimated 100 kg N, 14 kg P, 134 kg K, 179 kg Ca, 15 kg Mg and 10 kg S; in India the estimated amount of nutrients removed by a similar crop was 110 kg N, 25 kg P, 40 kg K, 45 kg Ca and 30 kg Mg. Fertilizers have little effect on the oil content of the foliage. Where irrigation facilities are available for other crops in a rotation, supplemental irrigation is recommended during dry periods and to promote regrowth after harvesting. The economic life of a well-managed plantation can be 10 years. It should not be less than 5–7 years as the cost of establishment is high. After this period rotation with other crops is recommended.
Diseases and pests
In Pelargonium Rosat Group diseases generally cause more damage than pests. The most damaging are leaf diseases such as anthracnose (caused by Glomerella, Gloeosporium and Colletotrichum spp.), leaf spot (caused by Alternaria, Cercospora, Fusarium spp.), and rust (caused by Puccinia pelargonii-zonalis). Pelargonium vitifolium (L.) L'Hér. has good resistance to anthracnose and has been used in breeding programmes in Réunion. Root and stem rots may cause severe damage in newly planted fields, but can be controlled by dipping cuttings in a fungicide solution before planting. Established plants may become infected when soil moisture is high or during periods of high air humidity. Frequently recorded causal agents include Xanthomonas pelargonii causing black rot, Pythium spp. causing root rot and Sclerotinia spp. causing stem or root decay. Spraying a fungicide along the plant row after harvesting can often contain an outbreak. Resistance to some diseases has been found in Indian selections and in ornamental cultivars. Several pathogenic viruses have been isolated from Pelargonium, thus only virus-free cuttings should be used for propagation. Nematodes have been recorded, but seem to cause only limited damage, possibly because geranium oil has nematicidal properties.
Pelargonium plants grown for essential oil are much less affected by insects than ornamental cultivars. A large number of insects including aphids, caterpillars, myrids, scale insects and whiteflies have been recorded, but rarely justify spraying with insecticides, especially as the residues of many insecticides adversely affect the quality of the oil.
Under favourable conditions the first harvest of Pelargonium Rosat Group can be made when the crop is 6–8 months old. Cutting too early may kill plants or retard regrowth. Subsequently, harvesting is done 2–3 times per year. To obtain maximum oil yield the crop should be sampled regularly to determine its oil content, but cutting time is normally related to plant height and flowering. Cutting is done manually or mechanically, normally at 12–20 cm above the ground. Field trials should establish the optimum cutting height, as nearly all oil is contained in the top 15 cm of a plant. Harvesting is best done during slightly overcast, but dry weather. Heavy rain or several misty days can reduce oil content to half; cutting should then be suspended until oil content has recovered. Cut branches should be loaded directly into a cart. Any contamination with soil, especially if rich in iron or aluminium, can affect oil quality.
Annual herbage yields of Pelargonium Rosat Group in Réunion are 15–30 t/ha, the average being 18 t/ha, yielding 5–20 kg oil. In India yields average 6–10 t/ha and may reach 20 t/ha.
Handling after harvest
Wilting of the herbage of Pelargonium Rosat Group before distillation may increase still efficiency, but should be carefully managed to avoid contamination with soil and loss of oil due to intense insolation. Geranium oil is obtained by water or steam distillation, the distillation method having little influence on oil quality. In Réunion the oil is produced by peasants operating small simple stills. The desired quality of the oil is maintained by traders who mix numerous small lots of oil. Modern steam-distillation equipment is loaded directly or after chopping the herbage. The load should not be too densely packed as this will channel the steam and cause local overheating. Since significant quantities of aroma compounds remain in the distillation water, cohobation is used. Up to 25% of the oil yield may be obtained from solvent extraction of the distillation water. This ‘secondary oil’ has a higher free alcohol content, but contains less ester. Water remaining in direct-fired water stills contains a different oil. This oil should be discarded as it contains undesirable compounds, probably as a result of overheating. Crude oil should be dried, filtered and stored in opaque containers, preferably at a temperature below 10°C. At higher temperatures the ester content decreases and the content of acids increases.
Solvent extraction of herbage yields a concrete that for most purposes should be distilled with alcohol to remove wax.
Germplasm collections of Pelargonium Rosat Group have been established at the Horticultural Research Station, Kodaikanal, India and at the Indian Institute of Horticultural Research, Bangalore, India. Morphological and yield (herbage and oil) studies have been made to identify promising strains.
Breeding work in Pelargonium Rosat Group is hampered by male sterility in most cultivars. Most breeding work has therefore relied on selection of superior plants. Cultivars with a high yield potential and high oil content have been selected in India, e.g. PG-7, PG-20, Alg-4n. Tolerance of heavy rainfall conditions and associated tip rot has also been found in some cultivars. Cultivars with high geraniol content and a moderate resistance to wilt have been identified in Egypt. In India a mutant characterized by fertile stamens and gigas traits has been found in a cultivar originally from Réunion. Hybrids between this mutant and a seed-setting cultivar (Alg-4n) form the basis of a breeding programme.
Because of the strong demand for geranium oil, Pelargonium Rosat Group will remain an important crop. Its adaptability to tropical conditions, and the relative uniformity of geranium oil from different origins seems to justify testing this crop in parts of the tropics where it is not yet cultivated and the basic ecological requirements prevail. More research is needed to demarcate the cultivar-group more clearly and to clarify its origin and affinity, which is essential for developing successful breeding programmes.
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Sources of illustration
• Oyen, L.P.A. & Nguyen Xuan Dung (Editors), 1999. Plant resources of South-East Asia No 19. Essential-oil plants. Backhuys Publishers, Leiden, the Netherlands. 277 pp.
Correct citation of this article:
Dasuki, U.A., 2002. Pelargonium Rosat Group. Record from Protabase. Oyen, L.P.A. & Lemmens, R.H.M.J. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, the Netherlands.
Pelargonium Rosat group – planted
Redrawn and adapted by PROSEA