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.
Grevillea polychroma Grevillea polychroma , commonly known as Tullach Ard grevillea, is a species of the plant genus "Grevillea". It is endemic to the state of Victoria in Australia. The taxon was first formally described as a subspecies of "Grevillea brevifolia " in 2000. It was promoted to species status in 2005. The species is listed as "Rare in Victoria" on the Department of Sustainability and Environment's "Advisory List of Rare Or Threatened Plants In Victoria".