Pelargonium () is a genus of flowering plants commonly called geraniums, pelargoniums, or storksbills. It includes about 280 species of perennials, succulents, and shrubs. Taxonomist Carl Linnaeus originally included all the species of Pelargonium and Geranium under the latter name. In 1789, Charles Louis L'Héritier de Brutelle separated them into two genera.
While Geranium species are mostly temperate herbaceous plants, dying down in winter, Pelargonium species are evergreen perennials indigenous to warm temperate and tropical regions of the world, with many species in southern Africa. They are drought and heat tolerant but can tolerate only minor frosts. Some species are extremely popular garden plants, grown as houseplants and bedding plants in temperate regions. They have a long flowering period, with flowers mostly in red, orange, or white, but intensive breeding has produced a huge array of cultivars with great variety in size, flower colour, leaf form and aromatic foliage.
Description
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 a 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 millimeters, up to several centimeters, and is an important floral characteristic in morphological classification. Stamens vary from 2 to 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.
Taxonomy
Pelargonium is the second largest genus (after Geranium) within the family Geraniaceae, within 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.
Genus history The name Pelargonium was first proposed by Dillenius in 1732, who described and illustrated seven species of geraniums from South Africa that are now classified as Pelargonium. Dillenius, who referred to these seven species with apparent unique characteristics as Geranium Africanum (African Geranium) suggested "Possent ergo ii, quibus novi generis cupido est, ea, quorum flores inaequales vel et irrregulares sunt, Pelargonia vocare" (Those who wish a new genus can therefore call those, whose flowers are unequal or irregular, ‘Pelargonia’). The name was then formally introduced by Johannes Burman in 1738. However Carl Linnaeus who first formally described these plants in 1753 did not recognise Pelargonium and grouped together in the same genus (Geranium) the three similar genera Erodium, Geranium, and Pelargonium. Linnaeus' reputation prevented further differentiation for forty years. The eventual distinction between them was made by Charles L’Héritier based on the number of stamens or anthers, seven in the case of Pelargonium. In 1774, P. cordatum, P. crispum, P. quercifolium and P. radula were introduced, followed by P. capitatum in 1790.
Circumscription Pelargonium is distinguished from the other genera in the family Geraniaceae by the presence of a hypanthium, which consists of an adnate nectar spur with one nectary, as well as a generally zygomorphic floral symmetry.
Subdivision De Candolle first proposed dividing the genus into 12 sections in 1824, based on the diversity of growth forms. (also available online at Gallica) 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; section Campylia (Lindley ex Sweet) de Candolle section Chorisma (Lindley ex Sweet) de Candolle section Ciconium (Sweet) Harvey section Cortusina (DC.) Harvey section Glaucophyllum Harvey section Hoarea (Sweet) de Candolle section Isopetalum (Sweet) de Candolle section Jenkinsonia (Sweet) de Candolle section Ligularia (Sweet) Harvey section Myrrhidium de Candolle section Otidia (Lindley ex Sweet) de Candolle section Pelargonium (Sweet) Harvey section Peristera de Candolle section Polyactium de Candolle section Reniformia (Knuth) Dreyer section Subsucculentia J.J.A. van der Walt
Phylogenetic analyses 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); subgenus Magnipetala Roeschenbl. & F. Albers Type: Pelargonium praemorsum (Andrews) F Dietrich subgenus Parvulipetala Roeschenbl. & F. Albers Type: Pelargonium hypoleucum Turczaninow subgenus Paucisignata Roeschenbl. & F. Albers Type: Pelargonium zonale (L.) L'Hér. in Aiton subgenus Pelargonium L'Hér. Type: Pelargonium cucullatum (L.) Aiton
Sixteen sections were then assigned to the new subgenera as follows, although many species remained only assigned to subgenera at this stage
subgenus Magnipetala 3 sections section Chorisma (Lindley ex Sweet) de Candolle – 4 species section Jenkinsonia (Sweet) de Candolle – 11 species section Myrrhidium de Candolle – 8 species subgenus Parvulipetala 3 sections section Isopetalum (Sweet) de Candolle – 1 species (Pelargonium cotyledonis (L.) L'Hér.) section Peristera de Candolle – 30 species section Reniformia (Knuth) Dreyer – 8 species subgenus Paucisignata 2 sections section Ciconium (Sweet) Harvey – 16 species section Subsucculentia J.J.A. van der Walt – 3 species subgenus Pelargonium 8 sections section Campylia (Lindley ex Sweet) de Candolle – 9 species section Cortusina (DC.) Harvey – 7 species section Hoarea (Sweet) de Candolle – 72 species section Ligularia (Sweet) Harvey – 10 species section Magnistipulacea Roeschenbl. & F. Albers Type: Pelargonium schlecteri Knuth – 2 subsections subsection Magnistipulacea Roeschenbl. & F. Albers Type: Pelargonium schlecteri Knuth – 2 species (P. schlecteri & P. luridum) subsection Schizopetala (Knuth) Roeschenbl. & F. Albers Type: Pelargonium afrum (Eckl. & Zeyh.) Steudel – 3 species (P. afrum, P. bowkeri, P. schizopetalum) section Otidia (Lindley ex Sweet) de Candolle – 14 species section Pelargonium L'Hér. – 34 species section Polyactium de Candolle – 2 subsections subsection Caulescentia Knuth – 1 species (Pelargonium gibbosum) subsection Polyactium de Candolle – 7 species
Subgenera 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.
Species
Pelargonium has around 280 species. Röschenbleck et al 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.
Etymology
The name Pelargonium is derived from the Greek πελαργός, pelargós (stork), because the seed head looks like a stork's beak. Dillenius originally suggested the name 'stork', because Geranium was named after a crane — "a πελαργός, ciconia, sicuti vocamus Gerania, γερανός, grus" (from pelargos, stork, as we call the Gerania, geranos, crane).
Distribution and habitat