Plant Biology

The Kingdom Protista (Protoctista) is a hodgepodge of organisms with little relationship to one another. Most members of this kingdom have features of one or more of the other kingdoms, but not enough to place them legitimately into any one of these as currently defined. Cladists (those who classify organisms based on cladistics) suggest rearranging the tree of life to accommodate the protista and redefining its branches based on gene sequencing and other new data. Three new kingdoms—each equal in rank to the present animals, fungi, and plants—would be added and the plant and animal kingdoms expanded to include the rest of the protista. The proposal is still in the pro versus con heated debate stage. This could be simply another esoteric controversy among biologists if not for the fact that the organisms under discussion are some of the most important in the world. Scores of protists are the single‐celled, photosynthetic, primary producers of marine and freshwater food chains—and have been for the past billion years. In addition, all of the protists provide basic clues to how life evolved on the early Earth; the kingdom is a collection of experiments on how to manage energy and conduct life. Within the protista are found the basic plans that were adopted, adapted, and modified into the life we see around us today.

With classifications in such a state of flux, which organisms one includes in the Kingdom Protista, and how to group them, are matters of choice. Table follows the lead of several popular textbooks. Animal‐like protists have been omitted from the table. They include such organisms as Sarcodina: amoebas, forams, radiolarians; Flagellates: dinoflagellates, euglenoids, zooflagellates (trypanosomes, Giardia); parasitic Sporozoans; and Ciliates like Paramecium. Those protists of particular interest to plant biologists usually include the fungi‐like and plant‐like organisms. As always, follow your instructor's views on the systematics of the protista.