How many scientific kingdoms are there

The idea that kingdoms should be defined in terms of ecological function was the origin of Whittaker's approach to the subject, and in his article, he tied this idea more explicitly to the ecosystem theory that had rapidly developed during the s Hagen , Golley , Kingsland Second, Whittaker argued for a classification system that was broadly evolutionary, although not necessarily phylogenetic.

Phylogenetic relationships were important but, according to Whittaker, monophyletic grouping needed to be balanced with other important criteria, such as ecological function and cellular organization.

In addition, Whittaker resisted a purely phylogenetic basis for classification because he considered many of the phylogenetic claims made by Copeland and other taxonomists to be highly speculative.

Before the widespread acceptance of cladistics, which did not occur until the s, Whittaker's views on phylogeny were held by many biologists. The differences between Whittaker's ecological approach and Copeland's traditional taxonomic approach are evident in the way they treated several important groups of organisms.

Both Whittaker and Copeland argued that the fungi should be removed from the plant kingdom, but for very different reasons. Whittaker created a separate kingdom for the fungi, not because the group was monophyletic, but because the fungi were united by their ecological role as multicellular decomposers in ecosystems.

This emphasis on decomposition as an ecological process worthy of defining a kingdom reflected Whittaker's own work with biogeochemical cycling and also the growing prominence of biogeochemistry in ecosystem ecology Hagen To further support a separate kingdom for the fungi, Whittaker pointed to recent research that cast doubt on the belief that modern fungi had descended from photosynthetic ancestors similar to filamentous algae. According to Whittaker, the evidence against this earlier claim undercut both the traditional grouping of fungi within the plant kingdom and Copeland's decision to combine the fungi with various algae in his kingdom Protoctista.

In place of the Protoctista, Whittaker now proposed a purely unicellular kingdom, Protista—an idea that he attributed to Ernst Haeckel. Although he acknowledged that many groups such as Chlorophyta had both unicellular and multicellular members, Whittaker argued that the distinction between unicellular and multicellular body plans was conceptually clear cut and biologically meaningful. Furthermore, Whittaker pointed to the symmetry between the multicellular kingdoms of animals, plants, and fungi and the various subgroups within the Protista.

In both cases, one could find the three major directions of evolution and ecological functions: producers, consumers, and decomposers. Therefore, by using two fundamental characteristics—mode of nutrition and cellular organization—Whittaker created a system of classification that was both simple and conceptually coherent figure 2.

The addition of kingdom Protista to Whittaker's original three-kingdom scheme highlighted another major difference between his ecological approach and Copeland's taxonomic approach.

Copeland restricted his plant kingdom to a monophyletic group of vascular plants and their close relatives. Whittaker originally wanted to include all producers in the plant kingdom. He was now willing to relegate unicellular algae and cyanobacteria to his new kingdom Protista, but Whittaker continued to place all multicellular producers in kingdom Plantae. Whittaker's functional plant kingdom was an admittedly polyphyletic group of land plants, brown algae, and red algae.

He justified this grouping on the grounds of both ecological function and cellular structure. Whittaker's delineation of the kingdoms Plantae and Protista was later rejected even by some of his strongest supporters Margulis , , but it highlights the distinction between his functional kingdoms and traditional taxonomic kingdoms.

It also illustrates the philosophical underpinnings of Whittaker's approach to classifying both kingdoms and communities. Just as one could not always use environmental variables to precisely determine whether an area would be forest or grassland, so one could not neatly place groups such as the Chlorophyta into one or another kingdom on the basis of cellularity figures 1 and 2.

Despite the ambiguity, Whittaker argued that his system provided the better alternative because it was conceptually more coherent than Copeland's system. Interestingly, later biologists tended to define kingdom Protista using a combination of criteria borrowed from both the Whittaker and the Copeland systems.

A decade later, Whittaker published his definitive five-kingdom system in the high-profile journal Science , ensuring that his ideas would reach a broad audience Whittaker Although the article repeated much of the line of reasoning that Whittaker employed in , there were several substantive differences in both content and style. Most importantly, Whittaker now accepted Copeland's earlier decision to place all prokaryotic organisms into their own kingdom.

Although he had considered this possibility in , Whittaker made the more conservative decision to include the bacteria as a subkingdom of the Protista.

The prokaryotic kingdom Monera now joined kingdoms Protista, Fungi, Plantae, and Animalia in the final version of Whittaker's system. Whittaker justified adding the new kingdom Monera to his system for several reasons.

By the end of the s, the prokaryote—eukaryote distinction was a mainstream idea accepted by leading microbiologists Sapp , , Citing the still-controversial endosymbiotic theory being championed by Lynn Margulis as an attractive explanation for the evolution of eukaryotic cells, Whittaker now claimed that the prokaryote—eukaryote boundary represented the most fundamental division in the living world. Finally, Whittaker argued that the absorptive nutritional mode that characterized most Monerans was the original method of gaining energy.

Photosynthesis had evolved in a few Monerans, but the three nutritional modes became well established only after the first eukaryotic protists evolved through endosymbiosis.

Therefore, organisms could be placed into one of three structural grades: prokaryotes, unicellular eukaryotes, and multicellular eukaryotes. Within the two higher grades, various lineages of producers, consumers, and decomposers could be clearly identified, although only producers and decomposers were found at the prokaryotic grade.

Stylistically, Whittaker departed from the broad review of competing systems that he had used in and presented classification as a choice between two alternatives: Copeland's four-kingdom system and Whittaker's new five-kingdom system. Both the importance of the choice and the rationale for making it were also new. Whittaker now emphasized the pedagogical importance of revising the traditional two-kingdom system with one that better represented the broad contours of the living world. Noting that several introductory biology textbooks questioned the plant—animal dichotomy, Whittaker had an obvious motivation for highlighting the differences between the two alternative replacements.

Compared with Copeland's elaborate taxonomic system, Whittaker claimed that his functional kingdoms rested on two criteria that biologists considered important and that students could easily understand. The Soviet launch of Sputnik 1 in served as a potent catalyst for educational change Grobman , Sundberg et al. Exploiting fears that the United States was falling behind the Soviet Union in science, educational reformers pushed for revamping the nation's outdated approach to biology.

Critics complained that existing textbooks were little more than dry surveys of plant and animal phyla, emphasizing anatomical description rather than unifying principles Grobman , Rudolph Highlighting how difficult this was, BSCS published three different high school textbooks because of disagreements over fundamental biological principles. Students were exposed to a variety of organisms but in the context of discussing these broader biological concepts, rather than as a taxonomic survey.

CUEBS never produced comparable products at the college level, but its recommendations influenced the writing of new college textbooks that were profoundly different from their predecessors Sundberg et al.

Popular pre-Sputnik textbooks were based on the pedagogical assumption that understanding topics such as genetics or ecology required a thorough familiarity with plant and animal taxa Johnson et al.

Therefore, chapters on heredity and ecology were tucked at the end of the book, where critics complained they were rarely read Rudolph Conscious of the educational reforms proposed by CUEBS, later editions of these established textbooks added more chapters on cell biology, genetics, and ecology Johnson et al.

By contrast, a new generation of post-Sputnik textbooks emphatically rejected this traditional pedagogical approach. Rather than detailed taxonomic and anatomical surveys, these books shifted much greater attention to cell biology, genetics, development, animal behavior, and ecology figure 3. These topics were organized around three overarching themes: evolution, the molecular and cellular basis of life, and energetics.

A comparison of coverage of topics in pre- and post-Sputnik introductory biology textbooks. The new design adopted by the authors of post-Sputnik textbooks posed serious challenges for discussing biodiversity.

The emphasis on unifying principles, combined with a much-reduced taxonomic survey, demanded a more compelling way to describe the broad classification of organisms than the traditional plant—animal dichotomy. By emphasizing the importance of both ecological trophic levels and cellular structure, Whittaker's five-kingdom system organized biological diversity using the very themes that new biology textbooks stressed so heavily. Still, the two most popular post-Sputnik textbooks did not immediately adopt Whittaker's system but only gradually came to embrace it in later editions.

Examining this transition sheds light on the difficulties of presenting biodiversity in the context of a new biology that deemphasized traditional taxonomy and the study of organisms. William Keeton was an invertebrate taxonomist, but he also turned a boyhood interest in training homing pigeons into a successful research career in avian orientation and navigation at Cornell University Emlen When the life sciences were reorganized at Cornell, Keeton moved from the Department of Entomology to a newly established program in Neurobiology and Behavior.

During this period, he designed and taught an extremely popular introductory biology course and spent five years writing his highly successful textbook Keeton , Emlen In some ways, Keeton's , Biological Science was a major departure from older textbooks, but it initially retained the traditional focus on plants and animals.

Indeed, Keeton's teaching innovation was combining botany and zoology into a single course Emlen , and this was reflected in the textbook that he wrote. Although he briefly discussed the kingdom Monera, Keeton stuck closely to the traditional taxonomic system of plants and animals. He acknowledged the weaknesses of the plant—animal dichotomy but justified his choice in two ways: First, organisms familiar to students tended to be either plants or animals, so the traditional two-kingdom system provided a common-sense way to organize biodiversity.

Most of the examples used by Keeton to illustrate unifying biological principles were drawn from multicellular plants and animals. Second, Keeton argued that phylogenetic relationships among protists and fungi were highly speculative and provided little support for newer classification systems. Although he briefly presented several alternative systems in a table, it was not until the third edition, in , that Keeton adopted Whittaker's five-kingdom system.

By this time, Whittaker, who was Keeton's colleague at Cornell, was acting as a consultant on the textbook. Not only did Keeton now use Whittaker's system to reorganize the five chapters on biodiversity, but he also devoted a page of the introductory chapter to discussing the logic of Whittaker's system in relation to the other major themes of the textbook.

Thus, the five-kingdom system joined natural selection, energetics, and cell theory as broad explanatory principles that provided the foundation for discussing all of the other topics in the book.

This approach was widely copied by later biology textbooks. Curtis was a highly successful science writer, who made up for a lack of professional training in biology by enlisting a lineup of distinguished scientists as consultants. The result of this collaboration was a textbook widely acclaimed for its engaging style Luria , Villager Curtis initially dismissed the choice of kingdom classification as a technical matter of interest only to professional taxonomists Curtis Like Keeton, she emphasized that phylogenetic relationships—particularly among the protists—were highly speculative.

Because there was little compelling support for any of the competing systems, Curtis was ambivalent about her choice of adding a third kingdom of microorganisms to the traditional plant and animal kingdoms. Despite her initial reluctance to strongly endorse any system of kingdom classification, Curtis's approach to introducing biological concepts harmonized well with the logic of Whittaker's approach. The hybrid hypothesis might explain the perplexing variation in needle number for P.

Foxtail pines Pinus balfouriana on the 11, ft m slopes of Alta Peak. The 13, ft. Left: Seed cones of cypress Cupressus from groves in southern California. Tecate cypress C. Sargent cypress C. Piute cypress C. Cuyamaca cypress C. Smooth-bark Arizona cypress C. Rough-bark Arizona cypress C. Right: Seed cones of cypress from groves in central and northern California.

Monterey cypress C. Gowen cypress C. Santa Cruz cypress C. Mendocino cypress C. Macnab cypress C. Modoc cypress C. Male pollen cones of the Piute cypress Cupressus nevadensis [syn. Each scalelike leaf bears a dorsal gland that exudes a resin droplet red arrow.

Interior cypress species such as this one typically have glaucous, resinous foliage, presumably an adaptation to dry, arid habitats. Foliage and pollen cones of the Smooth-bark Arizona cypress Cupressus glabra [Syn. Foliage of the Tecate cypress C. The scalelike leaves of Arizona cypress are glaucous and very glandular sticky.

The scalelike leaves of Tecate cypress are green and without dorsal resin glands. Right: Grove of Piute cypress C. The Piute cypress are more drought resistant, with gray glaucous , glandular resinous foliage similar to the Arizona cypress. In fact, some botanists now consider the Piute cypress to be a subspecies of the Arizona cypress and have named it C. This species typically grows on outcrops of serpentine in the Coast Ranges of central and northern California.

Serpentine is a shiny rock with a waxy luster and feel. It varies in color from creamy white and shades of green to black. In California, many species of rare and endangered plants are endemic to serpentine outcrops.

Genetic drift has undoubtedly occured in isolated cypress groves such as this one, which are often referred to as "arboreal islands. Podocarpus gracilior , a member of the Podocarpaceae native to eastern Africa. Although it is sometimes called "fern pine" it does not belong to the genus Pinus ; however, like pines and other cone-bearing species, it does belong to the Division Coniferophyta.

Minute female cones are composed of reduced scales, but usually only one scale bears an ovule that matures into a seed. There is little resemblance to a cone in the mature seed.

The seed has a hard coat surrounded by a fleshy outer layer aril. Supplement Historically, kingdom is the highest taxonomic rank, or the most general taxon used in classifying organisms.

However, in the new three-domain system introduced by Carl Woese in , the domain is the most general taxon , and kingdom is only next. It became the basis for newer multi-kingdom systems such as the six-kingdom system of Carl Woese and colleagues in The five biological Kingdoms by Robert Whittaker : Kingdom Monera : the most primitive of the five kingdoms that includes all the bacteria , also called monerans, which are single-celled prokaryotic organisms.

In six-kingdom system, Kingdom Monera is split into two kingdoms: 1 the Eubacteria , which are all bacteria apart from the archaebacteria , and 2 the Archaebacteria , which are single-celled organisms that live under extreme environmental conditions and have distinctive biochemical features Kingdom Protista : composed of single-celled and multicellular eukaryotes without the highly specialized tissue s.

See also: taxonomy. Fun Facts about Fungi. Some fungi taste great and others can kill you! Fungi are organisms that biologists once confused with plants, however, unlike plants, fungi cannot make their own food. Most obtain their food from parts of plants that are decaying in the soil. Slime molds and algae are protists. Sometimes they are called the odds and ends kingdom because its members are so different from one another. Protists include all microscopic organisms that are not bacteria, not animals, not plants and not fungi.

Most protists are unicellular. You may be wondering why those protists are not classified in the Archaebacteria or Eubacteria kingdoms. It is because, unlike bacteria, protists are complex cells. These delicate looking diatoms are classified in the protist kingdom. The Six Kingdoms When Linnaeus developed his system of classification, there were only two kingdoms, Plants and Animals.