Grasses were a diverse group of plants from Earth, which included the grains. Grass-like plants were also found on many other planets. Grass that was cut, dried and used for animal feed was called hay.
The Xyrillians grew grass on the floors of their starships. Charles Tucker III once noted the gasses they emitted helped the Xyrillians metabolism, and smelled like a "freshly mowed lawn." (ENT: "Unexpected")