1. 2. 3. 4. 5.

21.   22. Except 15. & 16., images show the flower & leaf of each species.

1.&2. P. frutetorum        3.&4. P. capitatum          5.& 6. P. ribifolium           7.&8. P. glutinosum

9.&10. P. grandiflorum          11.&12 .Mint-pungent P. radens         13.&14.Rose-mint P. radens  

15. Scentless   16. P. quercifolium      17.&18. Mint P. radens            19.&20. Rose P. radens  

21.&22. Pungent P. radens

Functions and effects of geranium oil – Geranium oil exhibits anti-microbial and antifungal properties.

Geranium oils from different sources show different degrees of antibacterial action. Lis-Balchin (2002,

Geranium and Pelargonium) has compiled much information about the essential oils of Pelargonium and

provides most of the following information.

It is known amongst geranium growers that various types of Pelargoniums show varying resistance to insect

pests. Bud worms (larvae of moths – Lepidoptera) are a common pest of zonal geraniums but do not attack

ivy geraniums. White flies are a common pest of regal geraniums but are less common on zonal geraniums.

Mites are not common pests of Pelargonium. Studies have shown that the products of trichomes have two

effects on insects. One is mechanical (the trichomes are sticky and impede the movement of small organisms).

The other is chemical (anacardic acids produced in the trichomes are poisonous to mites and to a lesser extent

to aphids and white flies). The production of anacardic acids (the chemicals causing allergic skin rash in poison ivy

and cashew fruits) has been found in two of 16 species of Pelargonium (namely P. frutetorum and P. inquinans).

The ability to produce anacardic acid is controlled by a single dominant allele. Both of these named species are

involved in the ancestry of today’s zonal geraniums.

Other standard tests of geranium oils show antimicrobial (antibacterial and antifungal) properties. It appears

that the rosy scented geranium oil and camphoraceous (pungent) oil are more antibacterial, while the minty,

nutmeg and lemony oils show lower biological activity. Geranium oils are repellant to cockroaches, some flies

and some mosquitoes.

Essential oils of various types have been used in aromatherapy and massage therapy. Geranium oil has been

used this way, but "there are few clinical studies and none of them show a statistically-significant difference

between massage with and without" essential oils. (Lis-Balchin, p. 241)

Various Pelargonium species have been used in traditional medicine. These include treatment of diarrhea,

dysentery, coughs, skin ailments and intestinal worms. Pelargonium grossularioides has been used to induce

abortion. Using standard laboratory and medical techniques and tests, it has been shown that various geranium

essential oils and their constituents have an effect on animal muscles. Both scented oils (from § Pelargonium)

and non-scented oils (from § Ciconium – zonal and ivy geraniums, and regal geraniums) are active. "Geranium

oil and the components geraniol, linalool and citronellol produce a fall in blood pressure in experimental animals

but reliable observations from human experiments are not available." (Lis-Balchin, p. 129)

We hear much about antioxidants related to human health and nutrition, and various Pelargonium extracts

show antioxidant properties. Indeed, "the genus Pelargonium is a rich source of bioactive compounds having

applications as antibacterial, antifungal, and antioxidant agents in addition to their contribution to the food/

beverage, cosmetic and pharmaceutical sectors …" (Lis-Balchin, p. 141).

Geranium oil is used widely in the cosmetic industry and is considered a "masculine" fragrance. It is used in

perfumes, colognes, soaps and other cosmetics. It has been used to a limited extent in food preservation, but it

has been little studied. Folk recipes have used lemon and rose geraniums in cooking, baking and beverages and

whole books of recipes are available. The low toxicity of geranium oil lends itself to these uses.

Chromosome numbers – The cultivars used to produce geranium oil are normally sterile plants, which are

propagated vegetatively from cuttings. Therefore, the cultivars are clones and assumed to be genetically uniform.

The commonly grown cultivars are assumed to be hybrids between P. radens (an octoploid with 2n = 88) and

P. capitatum (a hexaploid with 2n = 66). In fact, the cultivars have 2n = 77 (a sterile heptaploid).

Many cultivars of scented geraniums/pelargoniums have been available over the years. Currently, the Geraniaceae

Nursery in Richmond, CA lists 141 cultivars and species.

In the past, cultivars have often been attributed to various species of Pelargonium without much knowledge of the

ancestry of the plants. A check of the chromosome numbers of the various species of scented geraniums (§ Pelargonium)

shows a wide range from 2n = 22 to 2n = 88.

        2n (diploid)                     4n (tetraploid)                     6n (hexaploid)                     8n = 88 (octoploid)

        alpinum                          glutinosum                           capitatum                             graveolens

        betulinum                       hispidum                                                                        radens

        citronellum                     panduriforme                                                                    vitifolium

        cordifolium                     papilionaceum

        crispum                          pseudoglutinosum

        cucullatum                      quercifolium

        denticulatum                   tomentosum







In many groups of plants, hybrids between individuals with different chromosome numbers do not occur.

In some species, hybrids do not even occur between species with the same chromosome number. However,

in the genus Pelargonium, hybrids between different species are quite common. A check of The Pelargonium

 Breeder - Pelargonium Crosses List (V. 1, # 1, 2003), reveals 17 different interspecific crosses of species in

the section Pelargonium. Ten of these are between species with 2n = 22 and seven are between species with

2n = 44. In addition, 11 interspecific crosses have been made successfully between species in the Pelargonium

section and other sections within the genus (namely, § Polyactium, § Glaucophyllum, § Ligularia including the

species P. bowkeri, P. grandiflorum, P. fruticosum, P. oblongatum, P. rapaceum, P. fulgidum. Most other

such crosses were unsuccessful however.

In three cases, offspring have been produced between species with different chromosome numbers. These are:

P. quercifolium (2n = 44) X P. capitatum (2n = 66)

P. ribifolium (2n = 22) X P. glutinosum (2n = 44)

P. vitifolium (2n = 88) X P. capitatum (2n = 66)

However, the following crosses between species with different chromosome numbers were not successful

and did not produce viable seeds or offspring.

P. crispum (2n = 22) X P. glutinosum (2n = 44)

P. radens (2n = 88) X P. fulgidum (2n = 22)

P. ribifolium (2n = 22) X P. capitatum (2n = 66)

P. ribifolium (2n = 22) X P. glutinosum (2n = 44)

The large number of cultivars of scented pelargoniums has been noted by a number of authors. The difficulty in

determining which plants are true species has troubled many who have tried to categorize them. In order to skirt

the taxonomic problems of which species are which, many authors have dealt with the scented cultivars by cate-

gorizing them by scent – rose, lemon, pungent, etc. While this seems like a solution – as noted earlier – the scent

of a given plant may vary because of the environmental conditions under which it was grown. In addition to the

plant’s genetic constitution, scientific analyses of the oils shows that there are many components and their relative

abundance changes depending on various environmental and cultural factors.

While the commercial cultivars grown for oil production appear to be sterile heptaploids (7x) hybrids, the parental

types are quite fertile and produce abundant numbers of seeds. The species P. capitatum, P. radens, P. graveolens,

and P. vitifolium are all polyploids with 6n or 8n. At least theoretically, these plants have the potential for having

6 or 8 genes for the same trait or characteristic in their individual genomes (total genetic composition). This then

would allow for a great deal of variation in the offspring even of self-pollinated flowers. Unfortunately, I am not

aware of any scientific studies of the genetics of scented pelargoniums.

From personal experience, volunteer plants (referable to P. radens or Radula) with the same leaf and flower

appearance/morphology can have very different scents – varying from lemon, lemon rose, rose, minty, pungent,

scentless. Volunteer seedlings appear in the pots of parental plants, neighboring pots, elsewhere in the garden and

germinate for years after the original plants have ceased to exist. With this in mind, it is no wonder that parental plants

are thought to change (having been replaced by vigorous volunteer seedlings in the same pot) or that new variants

(with varying numbers of alleles for the production of different essential oils) with different and novel scents can occur.

Plant breeders and geneticists recognize this condition as the "gene dosage effect". More alleles may result in more

essential oil production or different combinations of alleles may result in different scents. The number of genes and

alleles may come about through polyploidy or various "mistakes’ in the genome. In humans Down’s syndrome results

from an extra chromosome with deleterious consequences. On the other hand, different human populations vary in the

number of alleles for alpha amylase 1 and this affects the quantity of this enzyme in saliva and differential digestion of starch.

People have differing abilities in detecting and distinguishing scents/fragrances, so it is no wonder scented geraniums

present such a challenge. Without this variation in the human being, the perfume, cosmetic, wine and food industries

would be less interesting.

The last scientific word has not yet been heard on scented geraniums; in the meantime, one should enjoy their

olfactory gifts.





© 2016, Central Coast Geranium Society (CCGS )