In between Oxydendrum and Polygonum which one has  about 220 species?
Polygonum Polygonum is a genus of about 220 species of flowering plant in the buckwheat and knotweed family Polygonaceae. Common names include knotweed, knotgrass, bistort, tearthumb, mile-a-minute, smartweed and several others. In the Middle English glossary of herbs "Alphita" ( 1400-1425), it was known as ars-smerte. There have been various opinions about how broadly the genus should be defined. For example, Buckwheat ("Fagopyrum esculentum") has sometimes been included in the genus as "Polygonum fagopyrum".
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".