I considered asking this on English.SE, but decided against it, since it strictly applies to biological nomenclature, which not many of them will know about - particularly that of plants.
So, in animals, all families end in the suffix -idae - e.g. Hominidae, Apidae, Canidae or Laridae. When referring to members of a family, you can use the suffix -ids - e.g. hominids, apids, canids or larids.
However, plant families are usually named with the ending "aceae" - such as Poaceae, the grass family. If I want to refer to members of Poaceae (without just saying the common name), what do I say?