Geraniums P. graveolens Scientific classification Kingdom: Plantae Division: Angiospermae Class: Magnoliopsida Order: Geraniales Family: Geraniaceae Genus: Pelargonium
Pelargonium capitatum (L.) L'Hér. ex Aiton
Pelargonium quercifolium(L. f.) L'Hér. ex Aiton
Pelargonium ×domesticum L.H. Bailey (pro sp.)
Pelargonium ×hortorum L.H. Bailey (pro sp.)
Pelargonium ×nervosum Sweet
Pelargonium /ˌpɛlɑrˈɡoʊniəm/ is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as scented geraniums or storksbills. Confusingly, Geranium is the correct botanical name of a separate genus of related plants often called Cranesbills. Both Geranium and Pelargonium are genera in the Family Geraniaceae. Linnaeus originally included all the species in one genus, Geranium, but they were later separated into two genera by Charles L’Héritier in 1789. Gardeners sometimes refer to the members of Genus Pelargonium as "pelargoniums" in order to avoid the confusion, but the older common name "geranium" is still in regular use, and most garden 'geraniums' are in fact 'pelargoniums', as opposed to true geraniums or cranesbill.
Species of Pelargonium are evergreen perennials indigenous to Southern Africa and are drought and heat tolerant, and can tolerate only minor frosts. Pelargoniums are extremely popular garden plants, grown as annuals in temperate climates.
The first species of Pelargonium known to be cultivated was Pelargonium triste, a native of South Africa. It was probably brought to the botanical garden in Leiden before 1600 on ships which stopped at the Cape of Good Hope. In 1631, the English gardener John Tradescant the elder bought seeds from Rene Morin in Paris and introduced the plant to England. The name Pelargonium was introduced by Johannes Burman in 1738, from the Greek πελαργός, pelargós, stork, because the seed head looks like a stork's beak.
Pelargonium leaves are usually alternate, and palmately lobed or pinnate, often on long stalks, and sometimes with light or dark patterns. The erect stems bear five-petaled flowers in umbel-like clusters called pseudoumbels. The shapes of the flowers have been bred to a variety ranging star-shaped to funnel-shaped, and colors include white, pink, red, orange-red, fuchsia to deep purple. The Pelargonium flower has a single symmetry plane (zygomorphic), which distinguishes it from the Geranium flower which has radial symmetry (actinomorphic).
The Mediterranean climate of southern Africa and Australia, and the north of New Zealand. Others are native to southern Madagascar, eastern Africa, Yemen, Asia Minor and two very isolated islands in the south Atlantic ocean (St. Helena and Tristan da Cunha). Most of the Pelargoniums cultivated in Europe and North America have their origins in South Africa. 
There is considerable confusion as to which Pelargoniums are true species, cultivars, or hybrids. The nomenclature has changed considerably since the first Pelargoniums were introduced to Europe in the seventeenth century. 
Commonly found are: Pelargonium crispum, Pelargonium cucullatum, Pelargonium echinatum, Pelargonium grandicalcaratum, Pelargonium graveolens, Pelargonium magenteum, Pelargonium x nervosum, Pelargonium odorantissimum, Pelargonium peltatum, Pelargonium quercifolium, Pelargonium tomentosum, Pelargonium tricolor, Pelargonium xerophyton, Pelargonium zonale.
Cultivars and hybrids
Horticultural pelargoniums (as opposed to botanical, the wild 'species') fall into six major groups, with zonals subdivided further. Thousands of ornamental cultivars have been developed from about 20 of the species.
The nine major groups are;
- Zonals which cover:
.. Fancy Leaf: Gold Leaf, Silver Leaf, Butterfly Leaf & Tri-Colour .. Fancy Flowered: Carnation Flowered, Tulip Flowered, Cactus Flowered, Rosebud Flowered .. Dwarf Zonals which are no taller than 8" when grown in a 4" pot .. Miniature Zonals which are no taller than 5" when grown in a 4" pot
- Angels (sometimes called miniature regals but they are not)
- Ivy-leaved (the varieties that trail and are used in hanging baskets or window boxes)
- Ivy x Zonals: a hybrid cross of ivy leaf and zonals
- Regals (sometimes wrongly referred to as 'Martha Washingtons')
- Frutetorum Hybrids
Ivy-leaved (Hanging) varieties are mainly derived from P. peltatum. Hanging stems and hardened leaves, used in hanging baskets.
Regal (Royal, French) varieties or P. × domesticum are mainly derived from P. cucullatum and P. grandiflorum. They have woody stems, wrinkled leaves and pointed lobes, and are mainly grown in greenhouses.
Zonal varieties, also known as P. × hortorum, are mainly derived from P. zonale and P. inquinans. They have round leaves with a coloured spot in the centre (hence Zonal).
The Garden geranium (Pelargonium x hortorum; syn. Pelargonium zonale) is one of the most common ornamental potted-plants, with over 500 varieties.
Scented-leaf varieties are derived from a great number of species, amongst others P. graveolens. These include; Species
- Almond - Pelargonium quercifolium
- Apple - Pelargonium odoratissimum
- Coconut - Pelargonium grossalarioides (Pelargonium parriflorum)
- Lemon - Pelargonium crispum
- Nutmeg - Pelargonium fragrans (Pelargonium x fragrans)
- Old Spice - Pelargonium fragrans 'Logees'
- Peppermint - Pelargonium tomentosum
- Rose - Pelargonium graveolens (Pelargonium roseum)
- Rose - Pelargonium capitatum
- Rose - Pelargonium radens
- Lemon Scented - Pelargonium citronellum
- Southernwood - Pelargonium abrotanifolium
- Strawberry - Pelargonium scarboroviae (Pelargonium x scarboroviae)
- Pelargonium ionidiflorum
- Fiery flowered stork's bill Pelargonium ignescens Scarlet Unique Scented Geranium 
- 'Attar of Roses' - a cultivar of the Rose Geranium (Pelargonium capitatum)
- 'Crowfoot Rose' - a cultivar of the Rose Geranium (Pelargonium radens)
- 'Dr. Livingston' - a cultivar of the Rose Geranium (Pelargonium radens)
- 'Grey Lady Plymouth' - a cultivar of the Rose Geranium (Pelargonium graveolens)
- 'Prince Rupert' - a cultivated variety of the Lemon Geranium ( Pelargonium crispum)
- 'Ginger' - Pelargonium x torento (Pelargonium torento)
- 'Lemon Balm' - a hybrid: Pelargonium x melissinum (Pelargonium melissinum)
- 'Lime' - a hybrid: (Pelargonium x nervosum) (Pelargonium nervosum)
- 'Prince of Orange' - a hybrid: Pelargonium x citrosum
Other than being grown for their beauty, species of Pelargonium such as P. graveolens are important in the perfume industry and are cultivated and distilled for its scent. Although scented Pelargonium exist which have smells of citrus, mint, pine, spices or various fruits, the varieties with rose scents are most commercially important. Pelargonium distillates and absolutes, commonly known as "scented geranium oil" are sometimes used to supplement or adulterate expensive rose oils. The edible leaves and flowers are also used as a flavouring in desserts, cakes, jellies and teas. Studies show that Pelargonium sidoides is effective for cough.
Pelargoniums and insects
Pelargonium species are used as food plants by the larvae of some Lepidoptera species including Angle Shades. Pelargoniums are believed to deter mosquitoes.
The Japanese beetle, an important agricultural insect pest, becomes rapidly paralyzed after consuming flower petals of zonal geranium (Pelargonium x hortorum). The phenomenon was first described in 1920, and subsequently confirmed. Research conducted by Dr. Christopher Ranger with the USDA Agricultural Research Service and other collaborating scientists have demonstrated an excitatory amino acid called quisqualic acid is present within the flower petals and is responsible for causing paralysis of the Japanese beetle. Quisqualic acid is thought to mimic L-glutamic acid, which is a neurotransmitter in the insect neuromuscular junction and mammalian central nervous system.
DiseasesMain article: List of geranium diseases
- ^ Sunset Western Garden Book, 1995:606–607
- ^ a b c James K. Sayre. Scented Geraniums or Pelargoniums, 2003
- ^ Geraniaceae: The natural order of gerania, illustrated by coloured figures and descriptions; comprising the numerous and beautiful mule-varieties cultivated in the gardens of Great Britain, with directions for their treatment. Robert Sweet. Volume 1 of Geraniaceae: The Natural Order of Gerania, Illustrated by Coloured Figures and Descriptions : Comprising the Numerous and Beautiful Mule-varieties Cultivated in the Gardens of Great Britain, with Directions for Their Treatment. Ridgway 1822 : Pelargonium ignescens
- ^ Global Biodiversity Information Facilty: Geranium ignescens
- ^ Davis, J.J. 1920. The green Japanese beetle. New Jersey Department of Agriculture Circular. 30: 33.
- ^ Ballou, C. H. 1929. Effects of geranium on the Japanese beetle. Journal of Economic Entomology. 22: 289-293.
- ^ Potter, D. A. and Held, D. W. 1999. Absence of food-aversion learning by a polyphagous scarab, Popillia japonica, following intoxication by geranium, Pelargonium x hortorum. Entomologia Experimentalis et Applicata. 91: 83-88.
- ^ Held, D. W. and Potter, D. A. 2003. Characterizing toxicity of Pelargonium spp. and two other reputedly toxic plant species to Japanese beetles (Coleoptera: Scarabaeidae). Environmental Entomology. 32: 873-880.
- ^ Geraniums and Begonias: New Research on Old Garden Favorites (the March 2010 issue of Agricultural Research magazine.)
- ^ Ranger, C.M., Winter, R. E., Singh, A. P., Reding, M. E., Frantz, J. M., Locke, J. C., and Krause, C. R. 2011. Rare excitatory amino acid from flowers of zonal geranium responsible for paralyzing the Japanese beetle. Proceedings of the National Academy of Sciences. http://www.pnas.org/content/early/2010/12/29/1013497108.full.pdf+html
- ^ Usherwood, P. N. R. 1994. Insect glutamate receptors. Advances in Insect Biochemistry and Physiology. 24: 309-341.
- Maria Lis-Balchin, ed., Geranium and Pelargonium: History of Nomenclature, Usage and Cultivation. (Taylor and Francis, 2002) ISBN 0-415-28487-2
- Ellaphie Ward-Hilhorst, van der Walt and Vorster. Pelargoniums of Southern Africa 1988 (3 vols)
- Plants for use: Pelargonium
- Ranger, C.M., Winter, R. E., Singh, A. P., Reding, M. E., Frantz, J. M., Locke, J. C., and Krause, C. R. 2011. Rare excitatory amino acid from flowers of zonal geranium responsible for paralyzing the Japanese beetle. Proceedings of the National Academy of Sciences. http://www.pnas.org/content/early/2010/12/29/1013497108.full.pdf+html
- www2.arnes.si/~mstrli/pp.html - The Pelargonium Page: descriptions of botanical species with plant and habitat photos
- Pacific Bulb Society: Pelargonium (tuberous species)
- Garden plants
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