SOME THOUGHTS ON SCENTED GERANIUMS – Part 2 by Wayne Handlos
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
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