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The genus Geranium is represented in the New World by 137 species assigned to three subgenera: subg. Geranium with 127 species (eight introduced), subg. Erodioidea with three native species, and subg. Robertium with seven introduced species. Two species of subg. Geranium are native in the New World as well as elsewhere: G. erianthum occurs also in eastern Asia, and G. sylvaticum is widespread in Europe and western Asia. The greatest diversity is found in Mexico (36 native species) and Peru (34 native species). The Andes in Colombia and Ecuador also harbor many endemic species, but fewer species are found in other parts of South America as well as in Central America and North America north of Mexico. Geranium comprises mostly herbaceous perennials with aerial stems; however, some species are annuals, and some form small cushion-like plants or dwarf shrubs. The leaves are usually palmatifid or palmatisect, although a few species have digitate, tridentate, or even entire leaves. All species have actinomorphic, pentamerous flowers with ten stamens and the distinctive beaked fruit typical for the family. The nomenclature was reviewed for each taxon. Full synonymies and descriptions are provided as well as keys. Each species is illustrated and mapped. Eight neotypes, 44 lectotypes, and two epitypes are designated, and one new combination, Geranium seemannii subsp. repens, is proposed.
