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".
Aroideae Aroideae is a subfamily of flowering plants in the Araceae family. It is the largest subfamily in Araceae and consists of about 72 different genera, and 2,300 species. Many Aroideae have spiny pollen grains without a sporopollenin outer exine layer and lacking an aperture.