Many biologists contributed to classifying different plants species into their separate kingdoms. They classified the kingdom Plantae into various divisions based on the following criteria.
Linnaeus classified the flowering plants into 24 classes based on the number and position of stamens.
He included all non-flowering plants such as algae, lichens, fungi, mosses, and ferns into a separate class called cryptogamia.
But his system of classification had a few drawbacks such as he did not consider relationships, and placed unrelated families in one class.