The Collaborative International Dictionary of English v.0.48:

Begonia \Be*go"ni*a\ (b[-e]*g[=o]"n[i^]*[.a]), n. [From Michel
   Begon, a promoter of botany.] (Bot.)
   A genus of plants, mostly of tropical America, many species
   of which are grown as ornamental plants. The leaves are
   curiously one-sided, and often exhibit brilliant colors.
   [1913 Webster]

WordNet (r) 3.0 (2006):

begonia
    n 1: any of numerous plants of the genus Begonia grown for their
         attractive glossy asymmetrical leaves and colorful flowers
         in usually terminal cymes or racemes