Which of these names is a genus of plant that consists of grass species:  Poa or Gymnocladus?
Gymnocladus Gymnocladus (Neo-Latin, from Greek γυμνὀς, "gymnos", naked + κλάδος, "klados", branch) is a small genus of leguminous trees. The common name coffeetree is used for this genus.
Parnassia The genus Parnassia, also known as Grass of Parnassus or bog-stars, are plants in the family Celastraceae. The plants occur in arctic and alpine habitats, as well as in dune systems and fens, swamps, wet meadows, open seepage areas, moist woods, and across the Northern Hemisphere. It is actually not a grass, but an herbaceous dicot. The stalk of the plant can reach up to 8 in , the leaves up to 4 in and the petals can be up to 1.4 in wide. The flower has five white petals with light green venation. There are five three-pronged sterile stamens, each tipped with drop-like, false nectaries, which (along with the visual cue of veins) attract pollinating flies and bees.