In between Oxydendrum and Polygonum which one has  about 220 species?
Oxydendrum: Sourwood or sorrel tree, Oxydendrum arboreum, is the sole species in the genus Oxydendrum, in the family Ericaceae. Polygonum: Polygonum is a genus of about 220 species of flowering plant in the buckwheat and knotweed family Polygonaceae.
Polygonum