Simplify the following text for a Grade 10 native English-speaking person.
Original: In some classification systems they have been called Plantae , by expanding the traditional Plant Kingdom to include the green algae .
Simplified: In some classification systems they have been treated as a kingdom , under various names , e.g. Viridiplantae , Chlorobionta , or simply Plantae , the latter expanding the traditional Plant Kingdom to include the green algae .