Bot1320 Chapter 11 Taxonomy and Phylogeny
  1. Carolus Linnaeus introduced a system of classification, or taxonomy, for grouping and naming similar organisms in hierarchical categories (taxa).
    • Carolus Linnaeus published his Systema Naturae in 1758.

      This was the first scientific approach to classifying organisms.


    • • Taxonomy

      In the Linnaean taxonomy (grouping organisms into taxa), each species is identified by a binomial scientific name: its Genus and species.

      For example, Sciurus carolinensis for the Eastern gray squirrel, which also belongs in:

      • family Sciuridae,
      • order Rodentia,
      • class Mammalia.

      The binomial name for humans is Homo sapiens.


    • • Linnaeus named five species of oak from eastern North America, including Quercus phellos for Willow oak, and Quercus rubra for Red oak, based mainly on morphology.

    • • The seven Linnaean taxa are:

      • kingdom
      • phylum
      • class
      • order
      • family
      • genus
      • species

      A taxon above kingdom called domain was added later.

      Exercise:

     
  2. Using standardized scientific nomenclature avoids confusion that can arise from common names.
    • • Common names in North America may mean different organisms in Europe or Australia.

      "Corn" may mean Maize or Wheat.

      "Bear" may refer to a Grizzly or a Koala.

      "Robin" can be different species of birds: the America Robin is a thrush, while the European Robin is a flycatcher.

     
  3. Charles Darwin proposed a theory of evolution to explain the adaptation of organisms to their environment in a process called natural selection.
    • • (1809-1882) published The Origin of Species in 1859, after a five-year (1831-1836) voyage on the HMS Beagle.

    • • Evolution by natural selection.

      Thousands of sea turtle eggs are laid each season, but less than 10% survive to adulthood, and fewer will find a mate and reproduce.

      Darwin observed that many organisms produce more offspring than can survive to reproduce.

      He proposed natural selection as the process that allows a few individuals with "favorable variations" to survive and reproduce - and pass on those "variations" to offspring.

      Over time, accumulation of favorable traits results in adaptation of organisms to their environment.

      The long-term result is evolution of new species: an ancestral common ancestor may yield offspring that evolve into separate species.

     
  4. Taxonomy should reflect phylogeny, the evolutionary history of organisms based on descent from a common ancestor.
    • • A cladogram draws relationships based on phylogeny (shared ancestry) instead of morphology.
      A clade contains all the organisms descended from a common ancestor, and share a character.
      For example, all organisms descended from an ancestor that developed jaws constitute a large clade (ingroup); smaller clades later developed lungs, etc. Note:
      • Only animals that have jaws can have hair.
      • All animals with hair have jaws.
      • Thus, you cannot find an animal with hair but no jaws.
     
  5. The phylogeny of plants (Kingdom Plantae) reflects adaptation to terrestrial habitats.
    • • Plants evolved from ancestral algae that were multicellular, photosynthetic, and aquatic. Over time, plants adapted to survive the dry conditions on land.

      • Nonvascular plants lack efficient internal transport of fluids; sperm swim to eggs.
        Example: mosses live in damp habitat and are small.

      • Seedless vascular plants have vascular systems for internal transport.
        Example: ferns can live in drier soil.

      • Gymnosperms produce seeds but not flowers or fruits; sperm travel to eggs via pollen tubes.
        Example: pine seeds are enclosed in cones.

      • Angiosperms produce flowers and fruits that contain seeds.
        Example: grasses and forbs are adapted to arid conditions on land.

    • • A fertilized seed contains an embryo that will develop into a sporophyte.

      The endosperm (food supply) may be stored in embryonic leaves called cotyledons.

      Angiosperms can be classified into two groups.

      1. Monocots (corn) have one cotyledon.

      2. Dicots (bean) have two cotyledons that usually have absorbed the endosperm.
     
  6. Major Angiosperm families include:
    • Poaceae (Gramineae)
      • • Poaceae (Gramineae) (grass)

        • Round, hollow, jointed stems.

        • Linear leaves with open sheath and ligule at blade base

        • Inflorescence of small, apetalous flowers.

        • 3 large stamens, 2 plumose stigmas
       
    • Apiaceae (Umbelliferae)
      • • Apiaceae (Umbelliferae) (carrot, parsley)

        • Inflorescence forms a compound "umbel".

        • 5 sepals, 5 petals and 5 stamens.
       
    • Asteraceae (Compositae)
      • • Asteraceae (Compositae) (daisy, sunflower)

        • Composite inflorescence.

        • Sepals modified to form a pappus (tuft of hairs), often attached to fruit.
       
    • Fabaceae (Leguminosae)

    • • Fabaceae (Leguminosae) (pea, bean)

      • 5 petals form "banner", "wings", and "keel" in flower

      • Fruit forms a pod.

      • Leaves often pinnately or palmately compound.

      • Symbiotic Rhizobium in root nodules fix nitrogen.