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(Burm. f.) Sol. ex Aiton
(Burm. f.) Sol. ex Aiton
Pelargonium // is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as geraniums (in the United States also storksbills). 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. The confusion stems from Linnaeus originally including all the species in one genus, Geranium, but their later being separated into two genera by Charles L’Héritier in 1789.
Pelargonium species are evergreen perennials indigenous to Southern Africa, and are drought and heat tolerant, but can tolerate only minor frosts. Some species are extremely popular garden plants, grown as bedding plants in temperate regions.
Pelargonium occurs in a large number of growth forms, including herbaceous annuals, shrubs, subshrubs, stem succulents and geophytes. The erect stems bear five-petaled flowers in umbel-like clusters, which are occasionally branched. Because not all flowers appear simultaneously but open from the centre outwards, this is form of inflorescence is referred to as pseudoumbels. The flower has a single symmetry plane (zygomorphic), which distinguishes it from the Geranium flower, which has radial symmetry (actinomorphic). Thus the lower three (anterior) petals are differentiated from the upper two (posterior) petals. The posterior sepal is fused with the pedicel to form a hypanthium (nectary tube). The nectary tube varies from only a few milimeters, up to several centimeters, and is an important floral characteristic in morphological classification. Stamens vary from 2-7, and their number, position relative to staminodes, and curvature are used to identify individual species. There are five stigmata in the style. For the considerable diversity in flower morphology, see figure 1 of Röschenbleck et al. (2014)
Leaves are usually alternate, and palmately lobed or pinnate, often on long stalks, and sometimes with light or dark patterns. The leaves of Pelargonium peltatum (Ivy-leaved Geranium), have a thick cuticle better adapting them for drought tolerance.
Pelargonium is the second largest genus (after Geranium) within the Geraniaceae family, whithin which it is sister to the remaining genera of the family in its strict sense, Erodium, Geranium, and Monsonia including Sarcocaulon. The Geraniaceae have a number of genetic features unique amongst angiosperms, including highly rearranged plastid genomes differing in gene content, order and expansion of the inverted repeat.
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. Carl Linnaeus originally grouped together in the same genus (Geranium) the three similar genera Erodium, Geranium, and Pelargonium. The distinction between them was made by Charles Louis L'Héritier de Brutelle based on the number of stamens or anthers, seven in the case of Pelargonium.
The chemist, John Dalton, first realized that he was color blind in 1794 when he heard others describe the color of the flowers of the pink (Pelargonium zonale), as pink or red, when to him it looked either pink or blue, having no relationship to red at all.
Pelargonium is distinguished from the other genera in the Geraniaceae family by the presence of a hypanthium, which consists of an adnate nectar spur with one nectary, as well as a generally zygomorphic floral symmetry.
De Candolle first proposed dividing the genus into 12 sections in 1824, based on the diversity of growth forms. Traditionally the large number of Pelargonium species have been treated as sixteen sections, based on the classification of Knuth (1912) who described 15 sections, as modified by Van der Walt et al. (1977-1997) who added Chorisma, Reniformia and Subsucculentia.
These are as follows;
All subdivision classifications had depended primarily on morphological differences till the era of phylogenetic analyses (Price and Palmer 1993). However phylogenetic analysis shows only three distinct clades, labelled A, B and C. In this analysis not all sections were monophyletic although some were strongly supported including Chorisma, Myrrhidium and Jenkinsonia, while other sections were more paraphyletic. This in turn has led to a proposal, informal at this stage of a reformulation of the infrageneric subdivision of Pelargonium.
In the proposed scheme of Weng et al. there would be two subgenera, based on clades A+B, and C respectively and seven sections based on subclades. Subsequent analysis with an expanded taxa set confirmed this infrageneric subdivision into two groups which also correspond to chromosome length (<1.5 μ, 1.5-3.0μ), but also two subclades within each major clade, suggesting the presence of four subgenera, these correspond to clades A, B, C1 and C2 of the earlier analysis, A being by far the largest clade with 141 taxa. As before the internal structure of the clades supported monophyly of some sections (Myrrhidium, Chorisma, Reniformia, Pelargonium, Ligularia and Hoarea) but paraphyly in others (Jenkinsonia, Ciconium,Peristera). A distinct clade could be identified within the paraphyletic Polyactium, designated section Magnistipulacea. As a result Polyactium has been split up to provide this new section, which in itself contains two subsections, Magnistipulacea and Schizopetala, following Knuth's original treatment of Polyactium as having four subsections.
Thus Röschenbleck et al. (2014) provide a complete revision of the subgeneric classification of Pelargonium based on four subgenera corresponding to their major clades (A, B, C1, C2);
Sixteen sections were then assigned to the new subgenera as follows, although many species remained only assigned to subgenera at this stage
Subgenus Magnipetala: Corresponds to clade C1, with 24 species. Perennial to short lived, spreading subshrubs, rarely herbaceous annuals. Petals five, but may be four, colour mainly white. Mainly winter rainfall region of South Africa, spreading into summer rainfall region. One species in northern Namibia and Botswana. Two species in East Africa and Ethiopia. Chromosomes x=11 and 9.
Subgenus Parvulipetala: Corresponds to clade B, with 39-42 species. Perennials, partly annuals. Petals five and equal, colour white or pink to deep purplish red. Mainly South Africa, but also other southern hemisphere except South America. a few species in East Africa and Ethiopia. Chromosomes x=7-19.
Subgenus Paucisignata: Corresponds to clade C2, with 25-27 species. Erect sometimes trailing shrubs or subshrubs, rarely geophytes or semi-geophytes. Petals five and equal, colour pink to red sometimes white. Summer rainfall region of South Africa, spreading into winter rainfall region and northern Namibia, with a few species in tropical Africa, Ethiopia, Somalia, Madagascar, the Arabian Peninsula and Asia Minor. Chromosomes x=mainly 9 or 10, but from 4-18.
Subgenus Pelargonium: Corresponds to clade A, with 167 species. Frequently xerophytic deciduous perennials with many geophytes and succulent subshrubs, less frequently woody evergreen shrubs or annual herbs. Petals five, colour shades of pink to purple or yellow. Winter rainfall region of South Africa and adjacent Namibia, spreading to summer rainfall area, and two species in tropical Africa. Chromosomes x=11, may be 8-10.
Pelargonium has between 200 - 280 species. The Plant list currently accepts 250 species names. Röschenbleck lists 281 taxa. 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 17th century.
Pelargonium is a large genus within the Geraniaceae family, which has a worldwide distribution in temperate to subtropical zones with some 800 mostly herbaceous species. Pelargonium itself is native to southern Africa (including Namibia) and Australia. Southern Africa contains 90% of the genus, with only about 30 species found elsewhere, predominantly the East African rift valley (about 20 species) and southern Australia, including Tasmania. The remaining few species are found in southern Madagascar, Yemen, Iraq, Asia Minor, the north of New Zealand and isolated islands in the south Atlantic Ocean (Saint Helena and Tristan da Cunha) and Socotra in the Indian Ocean. The centre of diversity is in southwestern South Africa where rainfall is confined to the winter, unlike the rest of the country where rainfall is predominantly in the summer months. Most of the Pelargonium plants cultivated in Europe and North America have their origins in South Africa. 
The Japanese beetle, an important agricultural insect pest, becomes rapidly paralyzed after consuming flower petals of the garden hybrids known as "zonal geraniums" (P. × 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 the excitatory amino acid called quisqualic acid present within the flower petals 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.
A study by the Laboratory of Apiculture & Social Insects group at the University of Sussex on the attractiveness of common garden plants to pollinators found that a cultivar of Pelargonium × hortorum was unattractive to pollinators in comparison to other selected garden plants such as Lavandula (lavender) and Origanum.
Their main requirement is a warm, sunny, sheltered location. Many varieties will tolerate drought conditions for short periods. They are commonly seen in bedding schemes in parks and gardens, but can also be grown indoors as houseplants if given enough light. More compact erect and trailing varieties are ideal for window boxes and hanging baskets, in association with other half-hardy plants like lobelias, petunias and begonias. Thousands of pelargonium cultivars are available from garden centres or specialist suppliers during the spring and summer months. They are regular participants in flower shows and competitive events, with numerous societies devoted exclusively to their cultivation. They are easy to propagate vegetatively from cuttings.
Despite not being frost-hardy, pelargoniums are extremely easy to grow and to propagate, but are usually grown as annuals. As they are evergreen perennials, they can be kept in flower throughout the winter months in a sufficiently favoured spot (or indoors). There are even one or two fully hardy species from Turkey. There are a number of methods for successfully overwintering pelargoniums in cooler zones than their native habitats.
For large numbers of plants, and particularly soft-stemmed pelargoniums that cannot be kept in a semi-dormant state, softwood cuttings can be taken in late summer the old woody plants discarded. The cuttings are then planted, and once rooted overwintered in compost filled trays in well lit indoor sites, with minimal watering. If fed in late winter and the shoot tips pinched out to encourage bushy growth, they can be potted up in mid spring and placed outside once the risk of frost has passed.
For small numbers of plants or limited space, plants can be lifted before the first frost and cut back to 10cm (4in), and placed in potting compost in a well lit frost free location, with minimal watering, and then repotted in mid spring.
Suitable for pelargoniums with tough woody stems where there are large numbers of plants. Plants can be lifted and allowed to dry out in a frost free location, wrapped in newspaper or hung. In early spring the roots can be soaked, and the plants cut back and then potted up.
Large bush type floriferous evergreen pelargoniums grown for the richness and beauty of their large flower heads. The majority of those grown today have been hybridised in the last 50 years and tend to be very short jointed and compact thus requiring little work to achieve a floriforous well rounded plant. Flowers are single, rarely double in mauve, pink, purple or white. They have rounded sometimes lobed or partially toothed (serrated) leaves, unlike the Zonal groups, without any type of zoning.
The Regal Pelargonium group includes “Decorative” types which are the descendants of older, less compact, smaller flowered varieties that are more suited to outdoor conditions; and “Oriental” types, which are the result of crosses between Regals and members of the Angel group (see below). Some have bicolour foliage. In the USA they are often known as the ‘Martha Washington’ or ‘Lady Washington’ Pelargoniums.
Cultivars, the majority of which, originate from a cross between P. Crispum and a Regal variety in the early part of the 20th Century. Angels have grown in popularity in the last 30 years or so due mainly to an explosion of new varieties being released by specialist nurseries resulting from the work done by dedicated amateur hybridisers. These hybrisers have managed to obtain many new flower colour breaks and tighter growth habits resulting in plants suitable for all sorts of situations. ‘Angels’ basically have the appearance of a small Regal with small serrated leaves and much smaller flowers and are more compact and bushy. The group extends to include similar small leaved and flowered types but usually with P. Crispum in their parentage. They are mostly upright bush type plants but there are some lax varieties that can be used for basket or hanging pot cultivation. Often called "Pansy-faced" in the US. Some varieties have bicolour foliage.
Usually of lax growth (trailing), mainly due to the long thin stems, with thick, waxy ivy shaped stiff fleshy evergreen leaves developed by the species P. Peltatum to retain moisture during periods of drought. Much used for hanging pots, tubs and basket cultivation. In the UK the bulbous double headed types are preferred whilst on the European continant the balcon single types for large scale hanging floral displays are favoured. Ivy Leaved Pelargoniums embrace all such growth size types including small leaved varieties and genetic hybrid crosses, which display little or no zonal characteristics. May have bicolour leaves and may have flowers that are single, double or rosette.
Known as zonal geraniums because many have zones or patterns in the center of the leaves. Mostly bush type plants with succulent stems grown for the beauty of their flowers, traditionally red, salmon, violet, white or pink. Zonals are often the pelargoniums most confused with Geraniums particularly in summer bedding arrangements. This incorrect nomenclature is widely used in horticulture, particularly in North America. They may also be referred to as Pelargonium x hortorum. Flowers may be double or single. Zonal pelargoniums are tetraploid mostly derived from P. inquinans and P. zonale, together with P. scandens and P. frutetorum.  and include a variety of plant types along with Genetic Hybrids such as Hybrid Ivy leaved varieties that display little or no ivy leaf characteristics (the Deacons group), or the ‘Stellar’ varieties. There are hundreds of zonal pelargoniums available for sale. and like other cultivars are sold in series such as 'Rocky Mountain', each of which is named after its predominant colour, e.g. 'Rocky Mountain Dark Red'.
Fancy Leaf Zonal Pelargoniums – besides having green leaves with or without zoning, this group also have variable coloured foliage that is sometimes used in classifying for exhibition purposes, e.g. ‘Bicolour’, ‘Tricolour’, ‘Bronze’ or ‘Gold’. Other foliage types are: ‘Black’ or ‘Butterfly’. There are an increasing number of these plants with showy blooms;
Zonal Pelargoniums have many flower types as follows;
Shrubby evergreen perennials grown chiefly for their fragrance, may be species or cultivars but all must have a clear and distinct scented foliage. Scent is emitted when the leaves are touched or bruised with some scents aromatic, others pungent and in a few cases, quite unpleasant. Several of the scented leaved pelargoniums are grown for the oil ‘geranol’, which is extracted from the leaves and is an essential oil much used commercially in perfumery. The scent of some species growing in their natural habitat, acts as a deterrent to grazing animals who appear to dislike the emitted scent. Conversely, it also attracts other insect life to visit the bloom and pollinate the plant. The scented leaves can be used for potpourri and they also have a use as flavourings in cooking. Occasionally scented types can be found in the some of the other groups mentioned i.e. the Angels having P. Crispum in their genetic makeup can often have a strong citrus scent. Leaves are lobed, toothed, incised or variegated.
Bushy shrubby evergreen cultivars originating in the mid 19th century, all having P. fulgidum in their pedigree. May have bicolour foliage. Some types, popularly known in the hobby as ‘Hybrid Uniques’, have been crossed with Regal pelargoniums and, as a result of this cross, are much more floriferous. Unique in sense of not fitting into any of above categories.
The species are the forfathers of all the cultivar groups listed above. In general, the definition of a species is that it breeds true, and is to be found doing this in the ‘wild’. Species pelargoniums have a large diversity of characteristics in habit, shape, size and colour, which probably accounts for them having retained their popularity for more than 300 years.
A Primary Hybrid is recognised as being the resultant plant from a first time cross between two different known species. Examples are P x ‘ardens’ – from P. lobatum x P. fulgidum (1810). P x ‘glauciifolium’ – from P. gibbosum x P. lobatum (1822). Usually, but not always, primary hybrids are sterile.
Cultivars are derived from a great number of species, amongst others P. graveolens. These include: Species
Pelargoniums rank as one of the highest number of potted flowering plants sold and also in terms of wholesale value.
Other than being grown for their beauty, species such as P. graveolens are important in the perfume industry and are cultivated and distilled for their scents. 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. Scented-leafed pelargoniums can be used to flavor jellies, cakes, butters, ice cream, iced tea and other dishes, The rose-, lemon- and peppermint-scents are most commonly used. Also used are those with hints of peach, cinnamon and orange. Commonly used lemon-scented culinary species include P. crispum and P. citronellum. Rose-scenteds include P. graveolens and members of the P. ‘Graveolens’ cultivar group. Other species and cultivars with culinary use include the lime-scented P. ‘Lime,’ the lemon balm-scented P. ‘Lemon Balm,’ the strawberry-lemon-scented P. ‘Lady Scarborough’ and the peppermint-scented P. tomentosum.
In herbal medicine, Pelargonium has been used for intestinal problems, wounds and respiratory ailments, but Pelargonium species have also been used for fevers, kidney complaints and other conditions. Geranium (Pelargonium) oil is considered a relaxant in aromatherapy, and in recent years, respiratory/cold remedies made from P. sidoides and P. reniforme have been sold in Europe and the United States. P. sidoides along with Echinacea is used for bronchitis. P. odoratissimum is used for its astringent, tonic and antiseptic effects. It is used internally for debility, gastroenteritis, and hemorrhage and externally for skin complaints, injuries, and neuralgia and throat infections. The essential oil is used in aromatherapy. It is also used to balance the hormonal system, menstrual flow, and clean the body of toxins.
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