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. It is native to eastern North America, from southern Pennsylvania south to northwest Florida and west to southern Illinois; it is most common in the lower chain of the Appalachian Mountains. The tree is frequently seen as a component of oak-heath forests.
Amaranthus polygonoides Amaranthus polygonoides is a species of flowering plant. It goes by the common name of tropical amaranth.