Geraniaceae is a family offlowering plants placed in the orderGeraniales. The family name is derived from the genusGeranium. The family includes both the genusGeranium (the cranesbills, or true geraniums) and the garden plants called geraniums, which modernbotany classifies as genusPelargonium, along with other related genera.
The family comprises 830species in five to seven genera. The largest genera areGeranium (430 species),Pelargonium (280 species) andErodium (80 species).
Theflowers are generally regular, or symmetrical. They arehermaphroditic,actinomorphic (radially symmetrical, like inGeranium) or slightlyzygomorphic (with a bilateral symmetry, like inPelargonium). Thecalyx and thecorolla are both pentamerous (with five lobes),petals andsepals are free and distinct. Theandroecium consists in two whorls of fivestamens each, some of which can be unfertile; thepistil consists of five (less commonly three) mergedcarpels. The linearstigmas are free, and the ovary is superior. The nectaries are localised at the bases of the antesepalous stamens and are formed by the receptacle.[3][4]Pelargonium has only one nectary gland on the adaxial side of the flower. It is hidden in a tube-like cavity which is formed by the receptacle.[3][5] Flower morphology is conserved within Geraniaceae, but there is a large diversity in floral architecture.[3] Flowers are usually grouped incymes (e.g. inGeranium),umbels (e.g. inPelargonium) or, more rarely,spikes.
Thefruit is a uniqueschizocarp made of five (or three)achenes, in the lower part the achenes are inside the calyx, while the upper part (the stylar beak) is thestyle of the flower, looking like a kind of long beak over the achenes. When the fruit is mature the style breaks into five (or three) hygroscopically active (ready to absorb water) bristles that curl, causing the achenes to be released.
California lacksfilaments withoutanthers (called staminodes), but the lower half of the five fertile stamens is made much wider by a wing with a rounded top on each side of the narrow higher part of the filament that carries an anther.Geranium only has ten fertile stamens without wings and lacks staminodes, except forG. pusillum that only has five stamens.Monsonia only has fifteen fertile stamens, which are merged at their base into a ring or merged at their base in trios with the middle filament longer than the others, except forM. brevirostrata with only five stamens.Erodium has five staminodes and five fertile stamens, without wings.Pelargonium has ten filaments without wings, between two and seven of which are topped by anthers, while the remaining three to eight are staminodes lacking anthers, but it can easily be distinguished by having only one narrow tube-like nectary inside what looks like the flowerstalk.[2]
Geraniaceae andFrancoaceae are the two families included in the orderGeraniales under theAngiosperm Phylogeny Group (APG) classification (APG IV).[7] There has been some uncertainty in the number of genera to be included.Stevens gives seven genera listed here,[8] while Christenhusz and Byng[9] state five genera.
Stevens also lists foursynonyms ofGeranium:GeraniopsisChrtekNeurophyllodes(A. Gray) O. DegenerRobertianumPicardRobertiella
The Geraniaceae have a number of genetic features unique amongst angiosperms, including highly rearrangedplastidgenomes differing ingene content, order and expansion of theinverted repeat.[11]
Most species are found in temperate or warm temperate regions, though some are tropical.Pelargonium has its centre for diversity in theCape region inSouth Africa, where there is a striking vegetative and floral variation.
(in Italian) Sandro Pignatti, Flora d'Italia, Edagricole, Bologna 1982.ISBN88-506-2449-2
Bakker, F.T., Culham, A., Hettiarachi, P., Touloumenidou, T., Gibby, M., 2004. Phylogeny of Pelargonium (Geraniaceae) based on DNA sequences from three genomes. Taxon 53, 17–28.
