Plant Taxonomy:
the grouping of plants based on their presumed relationships.

What information is given by the third part of a scientific name?

A plant is a multicellular, eukaryotic, autotrophic organism.

Review the kingdoms of living things.

Nomenclature: applying names to plants.

• Common names are easy to pronounce and remember, but they are confusing because of their local nature.
• Scientific names are formal names accepted by scientists around the world. In botany, all three components of a scientific name are important:
  1. genus name
  2. species name
  3. authority - individual(s) responsible for the name.
  Components 1 and 2 are either italicized or underlined. An example: Quercus alba L.
• See one of several systems of botanical classification group names.
• Study this list of Greek and Latin root words and their meanings.
• Explore some interesting curiosities of biological nomenclature.

The Principle of Priority:

In general, scientific names published at the earliest date take precedence over names of the same rank published later. The first validly published name of a species (or other taxon) becomes its accepted scientific name.

In order to have a definite starting point, botanists have agreed that for flowering plants the starting point shall be Linnaeus' Species Plantarum, published in 1753.

The International Code of Botanical Nomenclature lists exceptions and additions to this rule. This code is supposed to keep botanists all over the world using the same system of names. However, there is disagreement over some plant groupings and today we have several proposed classification systems. Some of these systems have 20 or more principal groups of plants. Complicating matters farther, the major classification groups for botany and for zoology are different. There is a movement to adopt only one classification system, the BioCode for all types of living things. To avoid confusion as much as possible, most literature usually refers only to family names and the genus and species of individual plants.

The "Type" Method:

Botanists have adopted the following method to stabilize the determining characteristics of a species:
• The author of a species must designate a certain specimen as the Type Specimen of that species.
• The Type Specimen is not necessarily the most representative of the group, it merely best shows the element on which the name for the group was originally based.
• The Type Specimen fixes the strict concept of that species and the application of its name.
• The Type Specimen is carefully preserved in a herbarium accessible to research scientists.
• To allow for damage or destruction of the Type Specimen, a system for designating acceptable substitutes has been devised.

  Holotype (Type Specimen): The original specimen designated by the author. "Types" are the most valuable of all specimens. Syntype: One of two or more specimens used by the author of a taxon if no holotype was designated, or one of two or more specimens designated as Types simultaneously in the original publication. Paratype: Any specimen, other than the holotype, referred to in the original publication of the taxon. Lectotype: A specimen selected by a competent person from the original material studied by the author. Isotype: Any specimen, other than the holotype, that duplicates the holotype. The isotype must come from the same collection, with the same locality, date, and number as the holotype. Neotype: A specimen selected to serve as a substitute for the holotype when all material on which the name was based is missing.

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What kind of plant is a "forb"?

Plants may be grouped using the following characteristics:

• Does the plant have vascular tissues?
  • Nonvascular plants do not have specialized tissues for conducting food and water.
    • Division Bryophyta:
      • Mosses and Liverworts

  • Vascular plants have tissues for conduction food and water.
    • All other plants.

• Does the plant reproduce by forming spores or seeds?
  • Vascular plants that form spores.
    • Division Psilophyta:
      • Whisk ferns , found in the tropics.
    • Division Lycophyta:
      • Club mosses , small evergreen plants that look somewhat like tiny pine trees.
    • Division Sphenophyta:
      • Horsetails , have jointed stems and scalelike leaves which give them a gritty feeling.
    • Division Pterophyta:
      • Ferns , a diverse group including tiny aquatic plants to fern trees that reach a height of 25 meters.

  • Vascular plants that form seeds.
    • Gymnosperms form "naked seeds", they are not enclosed in fruit.
      • Division Cycadophyta:
        • Only about 100 species of cycads are alive today, most of which are found in the tropics.
      • Division Ginkgophyta:
        • The only living ginkgo example is Ginko biloba. The ginkgo is a hardy deciduous tree that is planted as an ornamental.
      • Division Coniferophyta:
        • Conifers are woody plants with needle or scale-like leaves that form cones. They include pines, cedars, junipers, redwoods , firs, and spruce.
      • Division Gnetophyta:
        • An odd group of cone-bearing plants with vascular systems more like angiosperms than gymnosperms. Two of the three genera are desert plants while the other is a tropical vine.
    • Angiosperms form their seeds enclosed in a fruit.
      • Division Anthophyta:
        • The flowering plants. There are almost 300,000 species of angiosperms, making them the dominate group of plants in the world today.
        • The division has two classes. Monocotyledoneae and Dicotyledoneae.

Plants are sometimes grouped using common names such as tree, shrub, forb, grass, etc. While these are not taxonomy groups, a breif description might be helpful.

Tree - Woody plants with one main stem or trunk.
Shrub - Woody plants with several stems growing from the ground.
Forb - Herbaceous flowering plants with broad leaves.
Grass - Herbaceous flowering plants with narrow leaves and jointed stems.
Succulent - Plants with thick, fleshy tissues in the leaves or stems for storing water.

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How are monocot flowers and dicot flowers different?

Plants may be grouped by their number of seed leaves (cotyledons):

• Monocots have one seed leaf.
  • About 90,000 species.
  • Includes a small number of woody palm trees.
  • Most are grasses and grains such as wheat, oats, corn, and rice.
• Dicots have two seed leaves.
  • Almost 200,000 species.
  • A diverse group from cactuses to forest trees.

Monocots and dicots are the two most important groups we will study this year. You must be able to recognize any plant belonging to these two groups. The following table and diagram give characteristics that can be used for identification.

Comparison of Monocots and Dicots
Monocotyledons	Dicotyledons
Embryo with 1 cotyledon, usually developing under ground	Embryo with 2 cotyledons, usually developing above ground
Roots usually fibrous	A primary root usually present
Growth is mostly herbaceous	Growth either herbaceous or woody
Vascular bundles scattered	Vascular bundles usually forming a ring
Leaves usually parallel-veined	Leaves usually net-veined
Flower parts usually in multiples of 3	Flower parts usually 4 or 5

 

Research Links:

• Plant classification - U.C. Berkeley
• Plant Systematics - MetaLab
• Index Nominum Genericorum - International Code of Botanical Nomenclature
• Plant evolution - U.C. Berkeley
• Linnean Herbarium - Swedish Museum of Natural History

 

 

 

 

 

 

 

   

 

The third part of a scientific name, known as the authority, gives the name of the person or persons responsible for the name.

 

 

 

 

 

 

 

   

 

Forbs are herbaceous flowering plants with broad leaves.

 

 

 

 

 

 

 

   

 

Monocot flowers have parts in multiple of 3's and dicot flowers have parts in four or five.