Pelargonium /ˌpɛlɑrˈɡoʊniəm/ is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as geraniums. Confusingly, Geranium is the correct botanical name of a separate genus of related plants often called cranesbills or hardy geraniums. Both genera belong to 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.
Pelargonium are evergreen perennials indigenous to Southern Africa, and are drought and heat tolerant, but can tolerate only minor frosts. They are extremely popular garden plants, grown as bedding plants in temperate regions.
The first species of Pelargonium known to be cultivated was P. 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 flower has a single symmetry plane (zygomorphic), which distinguishes it from the Geranium flower which has radial symmetry (actinomorphic).
Pelargonium are native to 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 (Saint Helena and Tristan da Cunha). Most of the Pelargonium cultivated in Europe and North America have their origins in South Africa.
Species, cultivars and hybrids
Regal Group: Karl Offenstein
Ivy-Leaved Group: Pelargonium peltatum
Zonal Group: Pelargonium hortorum
There is considerable confusion as to which Pelargonium are true species, and which are cultivars or hybrids. The nomenclature has changed considerably since the first plants were introduced to Europe in the seventeenth century.
Horticultural Pelargonium cultivars (as opposed to wild species) are classified into several major groups, with zonals subdivided further. Thousands of ornamental cultivars have been developed from about 20 of the species.
The 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
- Miniature Zonals
- Ivy-leaved (the cultivars that trail and are used in hanging baskets or window boxes)
- Ivy x Zonals: a hybrid cross of ivy leaf and zonals
- Frutetorum Hybrids
- Ivy-leaved (trailing) cultivars 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 (or 'zone') in the centre (hence 'Zonal'). One of the most common ornamental pot plants, with over 500 cultivars.
Cultivars 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 Pelargonium capitatum
- 'Crowfoot Rose' - a cultivar of Pelargonium radens
- 'Dr. Livingston' - a cultivar of Pelargonium radens
- 'Grey Lady Plymouth' - a cultivar of Pelargonium graveolens
- 'Prince Rupert' - a cultivar of Pelargonium crispum
- 'Ginger' - Pelargonium x torento
- 'Lemon Balm' - a hybrid: Pelargonium x melissinum
- 'Lime' - a hybrid: (Pelargonium x nervosum)
- 'Prince of Orange' - a hybrid: Pelargonium x citrosum
Other than being grown for their beauty, species such as P. graveolens are important in the perfume industry and are cultivated and distilled for its scent. Although scented pelargoniums 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.
Pelargonium species are used as food plants by the larvae of some Lepidoptera species including Angle Shades.
The Japanese beetle, an important agricultural insect pest, becomes rapidly paralyzed after consuming flower petals of the garden hybrids known as "zonal geraniums" (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.