Question: In between Oxydendrum and Polygonum which one has  about 220 species?
Context: 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". The Diawling National Park lies in south west Mauritania around the Senegal River delta.  During the rainy season, much of the park consists of large lakes.  It is known for having over 220 species of identified birds, including pelicans, black storks, and flamingos, and also for its fish. Limnophila is a genus of crane fly in the family Tipulidae.  It has about 220 species. About 220 species of "Eremophila" have been formally described and about 40 more have been discovered but not formally described.  The genus is endemic to Australia except that one species, ("Eremophila debilis") is also found in New Zealand. Acraea is a genus of brush-footed butterflies (family Nymphalidae) of the subfamily Heliconiinae.  It seems to be highly paraphyletic and has long been used as a "wastebin taxon" to unite about 220 species of anatomically conservative Acraeini.  Some phylogenetic studies show that the genus "Acraea" is monophyletic if "Bematistes" and Neotropical "Actinote" are included (see Pierre & Bernaud, 2009).  Most species assembled here are restricted to the Afrotropic ecozone, but some are found in India, Southeast Asia, and Australia. Blechnum (hard fern) is a genus of between 150–220 species of ferns with a cosmopolitan distribution, in the family Blechnaceae in the eupolypods II clade of the order Polypodiales.  By far the greatest species diversity is in tropical regions of the Southern Hemisphere, with only a few species reaching cool temperate latitudes in the Southern Hemisphere (notably "B. penna-marina", south to Cape Horn, Chile, the southernmost fern in the world) and Northern Hemisphere (notably "B. spicant", north to Iceland and northern Norway). The El Paso Zoo is a zoo located in El Paso, Texas.  The 35 acre facility houses animals representing over 220 species, including such critically endangered species as the Amur leopard and the Aruba rattlesnake.  The zoo is home to a sea lion exhibit, which hosts daily shows, as well as exotic animals from around the world with feature attractions such as the African Star train and the Hunt Family Desert Spring.  The zoo recently expanded in size with the addition on the new African Exhibit featuring lions, zebras, and giraffes. This list comprises 220 species of non-marine molluscs that have been recorded in the scientific literature as part of the fauna of the island of Great Britain.  These are terrestrial and aquatic gastropods, and aquatic bivalves; the list does not include species of molluscs which are considered to be fully marine, except for two marine pulmonate gastropods. 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. The Phalangodoidea are a superfamily of the harvestman infraorder Grassatores with three recognized families and 220 species.  It is not to be confused with the similarly spelled subfamily Phalangioidea, which is also a harvestman superfamily, but within the infraorder Eupnoi.
Answer: Polygonum