Question: Which is in the grass family, Pachypodium or Arrhenatherum?
Context: Pachypodium is a genus of succulent spine-bearing trees and shrubs, native to Madagascar and Africa.  It belongs to the dogbane family, Apocynaceae.  "Pachypodium" comes from a Latin form from Greek "pachus" (thick) and "podion" (foot) (or Gk podos, root form of pous, foot), hence meaning "thick-footed". Festuca octoflora (formerly "Vulpia octoflora), also called six-weeks fescue, pullout grass, sixweeks fescue, eight-flower sixweeks grass, eight-flowered fescue"'; is an annual plant in the grass family (Poaceae).  The common name "six week fescue" is because it supplies about 6 weeks of cattle forage after a rain. Redfieldia (blowout grass) is a monotypic genus in the grass family (Poaceae).  The sole species, Redfieldia flexuosa, is native to the central United States.  The grass can be found on sand hills.  The plants grow in small clusters, protecting each other from the harsh desert conditions. Anthoxanthum odoratum, also known as sweet vernal grass, holy grass, vanilla grass, or buffalo grass, is a flowering plant in the grass family Poaceae.  It is a short-lived perennial plant native to acidic grassland in Eurasia.  It is grown as a lawn grass and a house plant, due to its sweet scent, and can also be found on unimproved pastures and meadows.  'Odoratum' is Latin for 'odorous'. Pachypodium ambongense belongs to the dogbane family Apocynaceae, which has recently been merged with the milkweed family Asclepiadaceae.  It was first published as a species of the genus "Pachypodium" in 1924 by the botanist Henri Louis Poisson. Ixophorus is a genus of Latin American plants in the grass family.  The only recognized species is Ixophorus unisetus.  Some authors have included one or two other species in the genus, such as "I. pringlei", but these have more recently been reduced to synonymy.  Common names for "I. unisetus" include crane grass, turkey grass, Honduras grass, Mexican grass, Central America grass, hático (Colombia), zacate blanco (El Salvador, Honduras, Mexico), and zacate chompipe (Nicaragua). Arrhenatherum elatius, with the common names false oat-grass, tall oat-grass, tall meadow oat, onion couch and tuber oat-grass, is a perennial species of grass, common in the temperate regions of Europe. Ampelodesmos is a genus of Mediterranean plants in the grass family, which is known by the common names stramma, Mauritania grass, rope grass, and dis grass.  It is classified in its own tribe Ampelodesmeae within the grass subfamily Pooideae. Polytrias is a genus of Asian, African, and Pacific Island plants in the grass family, commonly called Java grass Batiki bluegrass, Indian murainagrass, or toto grass.  The only known species is Polytrias indica, native to West Africa (from Senegal to Cameroon), Seychelles, the Indian Subcontinent, southern China, Southeast Asia, New Guinea, Fiji, and Micronesia.  It is also cultivated as a lawn grass in other tropical regions, and naturalized in scattered locations in tropical North and South America. Arrhenatherum, commonly called oatgrass or button-grass, is a genus of Eurasian and North African plants in grass family.
Answer: Arrhenatherum