Begonia is a genus of perennial flowering plants in the family Begoniaceae. The genus contains more than 2,000 different plant species, distributed primarily across tropical and subtropical regions of Africa, Asia, and Central and South America, with Africa considered the center of origin. Some species are commonly grown indoors as ornamental houseplants in cooler climates, or cultivated outside in summertime for their bright colorful flowers, which have petals but no sepals.

With 2,000+ species, Begonia is one of the largest genera of flowering plants. The species are terrestrial (sometimes epiphytic) herbs or undershrubs, and occur in subtropical and tropical moist climates, in South and Central America, Africa, and southern Asia. Terrestrial species in the wild are commonly upright-stemmed, rhizomatous, or tuberous. The plants are monoecious, with unisexual male and female flowers occurring separately on the same plant; the male contains numerous stamens, and the female has a large inferior ovary and two to four branched or twisted stigmas. Flowers come in all colors other than blue, and range in size from tiny individual blossoms to blooms the size of dinner plates. In most species, the fruit is a winged capsule containing numerous minute seeds, although baccate fruits are also known. The leaves, which are often large and variously marked or variegated, are usually asymmetric such that their left side and right side are different sizes. The plants vary in size from less than a foot to the recently discovered Begonia giganticaulis which can exceed twelve feet (3.6 meters) in height.

The genus name Begonia was coined by Charles Plumier, a French monk and botanist after discovering six new species in the Antilles, which he named Begonia to honor Michel Bégon, a former governor of the French colony of Saint-Domingue (now Haiti). The first time the name Begonia was used in print was in 1700, in a publication by Joseph Pitton de Tournefort. In 1753, Carl Linnaeus merged the original six species into one (Begonia obliqua). It was published in Species Plantarum and the name has been used ever since.

Due to a lack of fossil evidence, it has been inferred based on phylogeny that begonias originated from the Paleogene to the Miocene, 20 million - 65 million years ago, with the most likely period being the period between the Middle Miocene and Oligocene. Africa is considered the center of origin for the species, but most extant species likely evolved during the Pleistocene.

The mid-miocene was a warm period, resulting in an expansion of many tropical plants into Asia, including, potentially, begonias. "One view is that the formation of the current diversity of hotspots on Begonia in China and Southeast Asia resulted from the migration and expansion of African ancestors through the Himalayas to the east. The Himalayan mountain range formed when the Asian and Indian tectonic plates collided 35 million years ago. The estimated time for the ancestors of Begonia to have arrived in the area is about 15 million years, which coincides with the emergence of the highest elevations in the Himalayas. Therefor, based on climactic characteristics, is it speculated that a significant area of the montane habitats at the north of the Indian continent might have acted as a bridge for Begonia migration toward the east, resulting in Into-China and Malay Archipelago becoming diversity hotspots for Begonia." The expansion into the Americas is likely similar, where they grow from southern Mexico to the tip of Argentina. It's thought that the African ancestors of Begonia dispersed into the neotropical region at least two separate times.

The following phylogenetic tree shows the relationships among sections of the genus Begonia.

Selected species:

The different groups of begonias have different care requirements, but most species come from tropical regions, so they and their hybrids require warm temperatures. Most are forest understory plants and require bright shade; few will tolerate full sun, especially in warmer climates. In general, begonias require a well-drained growing medium that is neither constantly wet nor allowed to dry out completely. Many begonias will grow and flower year-round except for tuberous begonias, which usually have a dormant period. During this dormant period, the tubers can be stored in a cool, dry place. Begonias of the semperflorens group (or wax begonias) are frequently grown as bedding plants outdoors. Wax begonias are very attractive, they adapt well when brought inside the house for overwintering and can live up to 4–5 years.