Fertile hybrids giving a long season of flowering from May to September (or October). Many have interesting foliage too.
This hybrid species is probably the most commonly encountered in gardens - but most people will have the wrong name for it! The two parents are Geranium endressii and Geranium versicolor, and many gardens will have a green leaved, mid-salmon pink flowered cultivar that they think is Geranium endressii, the majority will be the hybrid Geranium x oxonianum. Geranium endressii has plain green leaves and a creeping habit, Geranium versicolor has shiny green leaves with brown marks and is clump forming, Geranium x oxonianum almost always has the brown markings, though they may be very hard to see, and is clump forming but may seed to give the impression of vegatative spread.
There are now many named cultivars, probably over 100, and they are nearly all pink! There are a few white, and near-whites. Most of the variation comes from the type of flower, size of the plant, and most especially the pattern of brown markings on the leaves. Most forms grow to between 30cm and 60cm tall and about 50cm across, they will usually retain a clump of leaves overwinter though this will be smaller than the clump size in the growing season.
Geranium x oxonianum is usually grown in sun though it can tolerate light shade and will continue to flower okay in some shade. Soil type is not important as long as the extremes of dry and wet are avoided.