Pelargonium /ˌpɛlɑːrˈɡoʊniəm/[5] is a genus of flowering plants which includes about 280 species of perennials, succulents, and shrubs,[4] commonly known as geraniums, pelargoniums, or storksbills. Geranium is also the botanical name and common name of a separate genus of related plants, also known as cranesbills. Both genera belong to the family Geraniaceae. Carl Linnaeus originally included all the species in one genus, Geranium, and they were later separated into two genera by Charles Louis L'Héritier de Brutelle in 1789.
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.
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).[6][7]
Pelargonium occurs in a large number of growth forms, including herbaceous annuals, shrubs, subshrubs, stem succulents and geophytes.[8] 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.[9] For the considerable diversity in flower morphology, see figure 1 of Röschenbleck et al. (2014)[8]
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.[10]