structural:summarization, stylistic:style_transfer, structural:reformatting, structural:expansion, linguistic:paraphrasing
Five kingdoms

The differences between fungi and other organisms regarded as plants had long been recognised by some; Haeckel had moved the fungi out of Plantae into Protista after his original classification, but was largely ignored in this separation by scientists of his time. Robert Whittaker recognized an additional kingdom for the Fungi. The resulting five-kingdom system, proposed in 1969 by Whittaker, has become a popular standard and with some refinement is still used in many works and forms the basis for new multi-kingdom systems. It is based mainly upon differences in nutrition; his Plantae were mostly multicellular autotrophs, his Animalia multicellular heterotrophs, and his Fungi multicellular saprotrophs.

The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies. The five kingdom system may be combined with the two empire system. In the Whittaker system, Plantae included some algae. In other systems, such as Lynn Margulis 's system of five kingdoms, the plants included just the land plants (Embryophyta), and Protoctista has a broader definition.

Following publication of Whittaker's system, the five-kingdom model began to be commonly used in high school biology textbooks. But despite the development from two kingdoms to five among most scientists, some authors as late as 1975 continued to employ a traditional two-kingdom system of animals and plants, dividing the plant kingdom into subkingdoms Prokaryota (bacteria and cyanobacteria), Mycota (fungi and supposed relatives), and Chlorota (algae and land plants).