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Unit 1: Biodiversity (Organismal Groups)

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    Biodiversity refers to the diversity of living organisms. Botany, rather than strictly plant biology, includes the study of many different groups of organisms. This section begins by discussing the organization (classification) and naming (taxonomy) of these groups based on their evolutionary history and genetic relatedness. The following chapters explore the wealth of diversity, beginning with the unicellular prokaryotes and acellular viruses. The other chapters cover eukaryotic groups that are often distinguished based on life cycles, morphology, nutritional mode, and cellular composition.

    Fungi, officially classified in the same group as plants until 1969, are heterotrophic eukaryotes more closely related to animals. Other heterotrophic organisms once thought to be fungi, including the slime molds and water molds, are discussed in the Protists chapter. Protists include an unrelated assemblage of eukaryotes that simply don't fit in as plants, fungi, or animals. Some of these lineages engulfed photosynthetic organisms and gained chloroplasts. These include the brown algae and diatoms from one engulfing event, and the red algae and green aglae from another.

    The red and green algae share their ancestors with land plants. These terrestrial, multicellular organisms can be divided into four major groups based on important evolutionary adaptations: bryophytes, seedless vascular plants, gymnosperms, and angiosperms. The angiosperms are the most diverse and most recent lineage, containing nearly 90% of all plant species. Unlike other plants, angiosperms make flowers and fruits.

    Mushrooms growing among moss
    Figure \(\PageIndex{1}\): This photo includes many of the organisms mentioned above. The central mushrooms are part of a lichen relationship, Lichenomphalia umbellifera, which includes a fungus and a green alga. The mushrooms are surrounded by mosses (of the bryophytes), ferns (from the seedless vascular plants), and a branch from a conifer (belonging to the gymnosperms) lays across them. Among the mosses, microscopic diatoms can likely be found living epiphytically, as well as free-living cyanobacteria. Uncharacteristically, one of the few lineages not pictured here is angiosperms. Perhaps they are all growing upon a fallen tanoak or some other hardwood tree. Photo Credit: Richard Tehan, CC BY-NC.


    Content by Maria Morrow, CC BY-NC

    This page titled Unit 1: Biodiversity (Organismal Groups) is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha, Maria Morrow, & Kammy Algiers (ASCCC Open Educational Resources Initiative) .

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