Found throughout much of the world's tropical and subtropical regions, begonias (Begonia spp.) comprise 1,500 different species with new ones are being discovered and scientifically named even today. According to begonia taxonomist Mark A. Tebbitt, begonias have poor mechanisms to disperse their seeds and thus the species is commonly found in such small geographic areas. Interestingly, begonias grow naturally in all tropical regions except those on the Australian continent.
Begonias are flowering plants (angiosperms) that are dicotyledons, which means they produce two seed leaves when they germinate. The begonia family, Begoniacaeae, consists of only two genera: Begonia and Hillebrandia. Mark Tebbitt, in his book "Begonias," mentions that the begonia family is closely related to three other plant families based on DNA-based analyses during the 1990s. Taxonomically, begonias are relatives of the cucumber (Cucurbitaceae), datisca (Datiscaceae) and the tetrameles (Tetramelaceae) families.
Traditionally, the hundreds of begonia species have been classified into smaller groups or "sections" that generally organize begonias based on distinct evolutionary lineage and common unique physical characteristics. According to Tebbitt, in 1998 the then-known 1,403 species of begonias were placed into 63 sections. By 2005, the more than 1,500 species were placed into 66 sections. Tebbitt also notes that taxonomists use sections in order to speed up and simplify the identification of begonias.
Few gardeners use the taxonomic section subdivisions of begonias since a superb understanding of botanical adjectives (with Latin roots) and other jargon is needed. Instead, horticulturists traditionally grouped begonias on their physical features such as root types, presence of stems, and growth habits. The American Begonia Society recognized eight different groups of begonia: cane-stemmed, rhizomatous, Semperflorens-cultorum, shrub-like, Rex-cultorum, trailing/scandent, and thick-stemmed. Tebbitt states that Europeans grow fewer types of begonias and therefore group them into only five categories: Elatior, Lorraine, Semperflorens-cultorum, tuberous, and foliage.
The universally accepted binomial naming system of living things pertains to species of begonias. All wild (naturally occurring) begonias are assigned the genus (Begonia) name plus a specific epithet (the species name). For example, the holly-leaf begonia is known botanically as Begonia aconitifolia.
Mankind has relished in manipulating genetics to create interesting hybrid plants and the experimentation in the Begonia genus has yielded thousands of cultivated varieties (cultivars). New begonia varieties are made by crossing flowers on different plants to yield seeds. The seeds are sown in great numbers and then seedlings selected for an ornamental quality by the breeder and then vegetatively reproduced by tissue culture, or cuttings to make clones for sale in the marketplace. The American Begonia Society (ABS) is the international registration authority for the names and cultivars of begonias. Breeders register their newly developed begonias, assign a cultivar name and provide other key information to the ABS in order to create/manage a finite database of man-made begonia selections.