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".
Phyllanthus Phyllanthus is the largest genus in the flowering plant family Phyllanthaceae. Estimates of the number species in this genus vary widely, from 750 to 1200. "Phyllanthus" has a remarkable diversity of growth forms including annual and perennial herbs, shrubs, climbers, floating aquatics, and pachycaulous succulents. Some have flattened leaflike stems called cladodes. It has a wide variety of floral morphologies and chromosome numbers and has one of the widest range of pollen types of any seed plant genus.