Mycology 427R/527R


IMPORTANT POINTS TO REMEMBER ABOUT CLASSIFICATION


1. Classification is:

a way to describe the relatedness of organisms
a way to differentiate between organisms

2. Classification systems are evolving as more information is gathered about organisms that allow them to be compared.

Characters are features of an organism that can be used for comparison:
  • gross morphology - no, or low magnification, basic shapes, color, size of structures
  • anatomical features - higher mag., microscopic arrangements of tissue, spore structures
  • ultrastructural features - Electron microscopic features: internal structure arrangement,
    spore, hyphal ornamentation
  • biochemical pathways - eg. lysine biosynthesis pathway, AAA or DAP
  • nucleic acid sequences - ie. rDNA. These have led to major advances in classification. Led to development of a whole new branch of study "Molecular Systematics"


    • 3. Classification is heirarchical, with at each level, organisms at a lower level are group together based on common characters that distinguish them from other groups at that level.

    Kingdom Phylum Class Order Family Genus Species.

    4. Differences among Classification systems generally are at the higher levels where ideas differ as to how much to group organisms together.

    Woese - three kingdoms: Prokaryotae, Eukaryotae, Archaea

    Cavalier- Smith - eight kingdoms

    Margulis - five kingdoms: We are using a modified Margulis system of six kingdoms: Prokaryotae, Plantae, Animalia, Stramenopila, Fungi, Protoctista.

    5. A Tree to explain the relationship between organisms and their hypothetical ancestors is termed a "Phylogenetic Tree"1: A hypothesis of the genealogy of a group of organisms.


    6. The organisms that we will consider in this class are in 3 kingdoms by Margulis' system.

    This group of Organisms is said to be "Polyphyletic": They do not share a close common ancestor. Or to put it another way, there is not an ancestor that they share exclusive of other organisms.

    Although they are not closely related evolutionarily, we study these organisms in Mycology because they share some morphological, nutritional and ecological features.

    The Kingdom "Fungi" is said to be "Monophyletic" (Gr. mono=single, phylon = stock, race). It is a group that includes an ancestor and ALL its descendants.

    1 For an excellent discussion of Phyolgeny and detailed phylogenetic trees, check out the Internationally renowned "Tree of Life" Homepage. Information about fungal relationships can be found here. Site: http://tolweb.org/tree/phylogeny.html