You may be speaking of an ecology; where ferns, mosses and lichens colonize an area of ground. Or you may be referring to a taxonomic group such as Orchidaceae. Both uses are acceptable, but...
the rocky planets and the gas planets .answer 2 there are several ways to divide plants into subsets. Such as vascular and non-vascular. Or Monocots and Dicots. Or Aquatic and terrestrial.