The arrangement of plants and objects in the landscape can be metaphoric. A metaphor: that is when something IS the representation of the intended meaning, such as “that tree is my grandfather”. If that tree was “like” my grandfather, we’d have a simile; enough of English 101.
Deciding to use an object as a metaphor relieves the landscape designer of finding a literal representation. Literal representations, such as garden gnomes, fairies, angels, or Venus’, attach the viewer too securely to one meaning.
Rocks, shrubs, trees (dead or alive) that suggest mythic forms create a stronger and broader effect on the viewer. A shadowed doorway into a dark woodland cannot avoid suggesting a journey into the subconscious. This is clearly a different effect than the loud direct message sent by the entrance to the carnival fun-house.