Pelargonium is a genus of flowering plants which includes about 200 species of perennial, succulent, and shrub plants, commonly known as geraniums.
Confusingly, Geranium is the correct botanical name of a separate genus. Both genera are 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.
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 part of the flower looks like a stork's beak.
Other than grown for their beauty, species of Pelargonium such as P. graveolens are important in the perfume industry and are cultivated and distilled for their scent. Although scented Pelargonia exist which have smells of citrus, mint, or various fruits, the varieties with rose scents are the most important commercially. Pelargonium distillates and absolutes, commonly known as "scented geranium oil" are sometimes used to supplement or adulterate expensive rose oils.
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.
References : Wikipedia
Here is a collection of the hybrids i grow.