Geranium is a genus of 422 species of annual, biennial, and perennial plants that are commonly known as geraniums, hardy geraniums, or cranesbills. They are found throughout the temperate regions of the world and the mountains of the tropics, with the greatest diversity in the eastern part of the Mediterranean region.

The palmately cleft leaves are broadly circular in form. The flowers have five petals and are coloured white, pink, purple, or blue, often with distinctive veining. Propagation is by semiripe cuttings in summer, by seed, or by division in autumn or spring.

Geraniums are eaten by the larvae of some Lepidoptera species including brown-tail, ghost moth, and mouse moth. At least several species of Geranium are gynodioecious. The species Geranium viscosissimum (sticky geranium) is considered to be protocarnivorous.

Name

thumb|Floral diagram of a Geranium garden hybrid called ‘Ann Thomson’, showing 5 free sepals, 5 free petals, 10 free fertile stamens, and a superior ovary consisting of 5 merged carpels, with 5 style branches

The genus name is derived from Ancient Greek (géranos) 'crane'. The English name 'cranesbill' derives from the resemblance of the fruit capsule of some of the species to a crane's head and bill. The ovary portion forms the head and the prolonged stigma creates the appearance of a beak.

Description

The flowers are typically five-petaled and white to purple. The leaves are palmate divided into narrow, pointed segments.

Confusion with Pelargonium

thumb|upright=.9|The "bill" and seed dispersal mechanism of G.'pratense

Confusingly, "geranium" is also the common name of members of the genus Pelargonium, which are also in the family Geraniaceae and are widely grown as horticultural bedding plants. Linnaeus originally included all the species in one genus, Geranium, but they were later separated into two genera by Charles L’Héritier in 1789. Other former members of the genus are now classified in Erodium, including the plants known as filarees in North America.

The term "hardy geranium" is often applied to horticultural Geraniums to distinguish them from the Pelargoniums, which are not winter-hardy in temperate horticulture. However, not all Geranium species are winter-hardy (see below).

The shape of the flowers offers one way of distinguishing between the two genera Geranium and Pelargonium. Geranium flowers have five very similar petals, and are thus radially symmetrical (actinomorphic), whereas Pelargonium (and also Erodium) flowers have two upper petals which are different from the three lower petals, so the flowers have a single plane of symmetry (zygomorphic).

Cultivation

A number of geranium species are cultivated for horticultural use and for pharmaceutical products. Some of the more commonly grown species include:

  • Geranium albanum (crested cranesbill)
  • Geranium cinereum
  • Geranium clarkei (Clarke's geranium)
  • Geranium dalmaticum
  • Geranium endressii (Endres's cranesbill)
  • Geranium erianthum (woolly geranium)
  • Geranium fremontii (Fremont's geranium)
  • Geranium himalayense, often sold under Geranium grandiflorum
  • Geranium ibericum (Caucasus geranium),
  • Geranium macrorrhizum (bigroot cranesbill or bigroot geranium)
  • Geranium maculatum (wild geranium)
  • Geranium maderense (giant herb robert)
  • Geranium × magnificum (showy geranium)
  • Geranium phaeum (dusky cranesbill)
  • Geranium platypetalum (broad-petaled geranium)
  • Geranium pratense (meadow cranesbill)
  • Geranium psilostemon (Armenian cranesbill)
  • Geranium renardii (Renard geranium)
  • Geranium sanguineum (bloody cranesbill)
  • Geranium subcaulescens (grey cranesbill)
  • Geranium sylvaticum (wood cranesbill)

All the above species are perennials and generally winter-hardy plants, grown for their attractive flowers and foliage. They are long-lived and most have a mounding habit, with palmately lobed foliage. Some species have spreading rhizomes. They are normally grown in part shade to full sun, in well-draining but moisture retentive soils, rich in humus. Other perennial species grown for their flowers and foliage include: Geranium argenteum, G. eriostemon, G. farreri, G. nodosum, G. procurrens, G. pylzowianum, G. renardii, G. traversii, G. tuberosum, G. versicolor, G. wallichianum, and G. wlassovianum. Some of these are not winter-hardy in cold areas and are grown in specialized gardens like rock gardens. Geranium 'Johnson's Blue' is a hybrid between G. himalayense (southwestern China), with G. pratense (European meadow cranesbill).

Cultivars

thumb|Close up of a wet geranium cultivar (probably 'Johnson's Blue')

The following hybrid cultivars have gained the Royal Horticultural Society's Award of Garden Merit (other cultivars are dealt with under their species name - see above):-

  • 'Ann Folkard'
  • 'A. T. Johnson' (G. × oxonianum)
  • 'Ballerina'
  • 'Blue Cloud'
  • Blue Sunrise='Blogold' <small>(PBR)</small>
  • 'Brookside'
  • 'Danny Boy'
  • 'Dilys'
  • 'Gypsy' (G. × lindavicum)

<!-- AGM withdrawn *'Johnson's Blue'-->

  • 'Ivan'
  • 'Mavis Simpson'
  • 'Nimbus'
  • 'Orion'
  • Patricia='Brempat'
  • Rothbury Gem='Gerfos'
  • Rozanne='Gerwat'
  • 'Russell Prichard'
  • 'Sirak'
  • 'Wageningen'
  • 'Wargrave Pink' (G. × oxonianum)

<gallery>

File:Geranium maculatum - wild cranesbill - desc-flower straight on.jpg|Geranium maculatum, wild cranesbill

File:Wild Geranium (Geranium maculatum).jpg|Geranium maculatum

File:Illustration Geranium phaeum0.jpg|Geranium phaeum - from Thomé Flora von Deutschland, Österreich und der Schweiz 1885

File:Geranium platypetalum1.jpg|Geranium platypetalum

File:Geranium sanguineum0.jpg|Geranium sanguineum

File:Geranium pratense (Meadow Cranesbill).jpg|Geranium pratense (meadow cranesbill)

File:Geranium-robertianum(Samen).jpg|Geranium robertianum (herb robert)

File:GeraniumMaderense.jpg|Geranium maderense

File:Starr 980718-1820 Geranium arboreum.jpg|Geranium arboreum

File:גרניון גזור.jpg|Geranium dissectum

</gallery>

See also

  • List of Geranium species

References

Bibliography

  • Genus Geranium in North America: the Perennials
  • ITIS list of Geranium species
  • Geranium Taxonomic Information System