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WHY DO THOSE GERANIUMS SMELL LIKE THAT?       

By Wayne Handlos, Ph.D.

Images of molecular structures of essential oils and fragrance compounds not found in rose scented geraniums.

 

In "Why Do Rose Geraniums Smell That Way" , I listed the primary components of ‘geranium oil’, basically the compounds

which give rose geraniums their rosy/floral fragrance. But what about all of those other scented leaf geraniums (Pelargonium)?

 

Numerous studies have been conducted to determine the components of the essential oils produced by

other species and cultivars of the scented Pelargoniums. These compounds and their fragrance characteristics

are listed in the accompanying table. This has led to another classification of the scented geraniums

by Lis-Balchin. Namely five categories are recognized by her: rose, mint, peppery-pungent, citrusy, and

camphoraceous-pungent based on the predominant chemical produced by each. The rose category is characterized by the predominance

 of  the chemicals listed last month and includes such species as P. capitatum, P. radens, P. graveolens and the cultivars ‘Attar of Roses’,

 ‘Rosé’ and ‘Rober’s Lemon Rose’.

 

The mint category produces scents dominated by menthone and isomenthone and includes P. tomentosum (peppermint geranium),

‘Chocolate Peppermint’, and ‘Lady Plymouth.’ The peppery-pungent group includes P. vitifolium, P. papilionaceum and P. ‘Filicifolium’. The

distinctive chemical in these plants is citronellic acid. The citrusy group is characterized by producing the lemon/lime/orange scented

compounds like citronellol, geranial and neral. The familiar species and cultivars in this group include P. citronellum, P. crispum,

P. scabrum, ‘Lemon Fancy’ and ‘Mabel Grey.’

 

The camphoraceous-pungent group is a mixed bag of species and cultivars producing such fragrant compounds

as alpha thujene, alpha pinene, alpha terpineol, methyl eugenol, fenchone and p-cymene. Species

and cultivars in this group include P. glutinosum, P. x fragrans, P. odoratissimum, P. exstipulatum, P. quercifolium,

‘Clorinda’, ‘Copthorne’, ‘Village Hill Oak’ and ‘Sweet Mimosa’.

 

Obviously, different scents are detected depending on the proportions of the various compounds produced

by the different plants and hybridization can bring together different combinations of fragrant

compounds. On top of this there are the variations mentioned last week relating to the influences of

stage of growth, cultural practices and the effects of soil and weather.

Essential oils and fragrance compounds not found in the rose scented geraniums

Compound                 Fragrance                           Found in                     %

α pinene                    turpentine                           P. capitatum                 47

β pinene                    woody, pine, resinous      P. quercifolium            19

geranial                     strong lemon                      P. citronellum               42

neral                          sweet lemon                          ‘Lemon Fancy’           28

α phellandrene          peppery, woody                   ‘Chocolate Mint’        2-17

β phellandrene          peppery, minty                      ‘Sweet Mimosa’           5

citronellic acid           grassy, smokey                 P. vitifolium                76-83

geranic acid              weedy, musty, woody        P. papilionaceum          5

methyl eugenol          clove, spicy                        P. grossularioides       11

p-cymene                   turpentine, woody             P. glutinosum             16-23

limonene orange       citrus                                  P. glutinosum             2.8-13

hexenyl butyrate         buttery, fruity                     P. glutinosum                8-15

α thujene                     pungent, woody               P. x fragrans                     9

fenchone                    camphor, earthy, woody  P. x fragrans                     8

terpinen-4-ol               nutmeg                                 ‘Village Hill Oak’         11

α terpineol                  floral, lilac                          P. quercifolium              30

© 2010, Central Coast Geranium Society (CCGS )