Geranium is a genus of 422 species of Annual plant, Biennial plant, and Perennial plant that are commonly known as geraniums or cranesbills. They are found throughout the temperateness 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 Leaf are broadly circular in form. The flowers have five petals and are coloured white, pink, purple, or blue, often with distinctive veining. Geraniums will grow in any soil as long as it is not waterlogged. Propagation is by semiripe cuttings in summer, by seed, or by division in autumn or spring.
Geraniums are eaten by the of some Lepidoptera species including brown-tail, ghost moth, and mouse moth. At least several species of Geranium are gynodioecy.Hessing, M.B. 1989. Variation in self-fertility and floral characters of Geranium caespitosum (Geraniaceae) along an elevational gradient. Plant Systematics and Evolution 166:225-241.Van Etten and Chang 2014. Frequency-dependent pollinator discrimination acts against female plants in the gynodioecious Geranium maculatum Annals of Botany 114:1769–1778 The species Geranium viscosissimum (sticky geranium) is considered to be protocarnivorous.
The fruit capsule consists of five cells joined to a column produced from the centre of the flower. The cells form lobes which eventually separate, each containing one seed. When the fruit is ripe, the beak-like stigma springs open and casts the ovoid, streamlined seeds some distance, dispersing the seeds.
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).
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, Geranium farreri, Geranium 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).
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