Plants Used By People

Green plants - also known as Viridiplantae, Viridiphyta or Chlorobionta - Plantae sensu stricto - Includes the land plants plus Charophyta (i.e. stoneworts), and Chlorophyta (i.e., other green algae such as sea lettuce). Viridiplantae encompass a group of organisms that possess chlorophyll a and b, have plastids that are bound by only two membranes, are capable of storing starch, and have cellulose in their cell walls.
Archaeplastida, Plastida or Primoplantae - Plantae sensu lato - Comprises the green plants above plus Rhodophyta (red algae) and Glaucophyta (glaucophyte algae). This clade includes the organisms that eons ago acquired their chloroplasts directly by engulfing cyanobacteria.
Outside of formal scientific contexts, the term "plant" implies an association with certain traits, such as multicellularity, cellulose, and photosynthesis. Many of the classification controversies involve organisms that are rarely encountered and are of minimal apparent economic significance, but are crucial in developing an understanding of the evolution of modern flora.