PLANT CLASSIFICATION

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PLANT CLASSIFICATION
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Plant Classification - Overview

• Plant Systematics and Taxonomy
• - Species concept
• - Plant nomenclature
• - Higher/Lower order plant taxa
• Ecological Classification
• - Plant life forms/physiography
• - Plant life histories (plant strategy)
• - Ecological differentiation (ecotypes)

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Plant Taxonomic ClassificationTerminology

• Systematics the science of organismal
  diversity, involving the discovery, description,
  and interpretation of biological diversity.
• Taxonomy the science of organizing things
  (plants) into groups or taxa. The science of
  classification, a natural product of systematics

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Natural vs. Artificial Plant Classification

• Artificial involves the classification of
  plants based on traits that do not necessarily
  reflect their presumed evolutionary
  relationships.
• Natural (Phylogenetics) - the classification of
  organisms based on their inferred evolutionary
  relationships. Phylogenetic classification
  schemes tend to be hierarchial.

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Phylogenetics Traditional Traits

• Morphology Traditional plant phylogenies are
  based primarily on the evaluation of
  morphological traits, especially floral traits,
  several of which, are thought to be less
  susceptible to natural selection.
• Anatomical Important for some species,
  generally difficult to evaluate but be useful in
  instances.
• Chemical Analysis requires sophisticated
  analytical equipment, but may be important for
  certain lineages of plants.
• Problems shared by all susceptible to
  convergent evolution.

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Molecular Phylogenetics

• The study of phylogenetic relationships based on
  the evaluation of molecular (DNA, RNA, protein)
  data. Dominated by the evaluation of DNA
  sequence data.
• Types of DNA sequences evaluated
• 1. Coding sequences of RNA or proteins that
  provide critical metabolic function somewhat
  shielded from selection pressure (chloroplast
  enzymes, rRNA).
• 2. Non-coding gene regions (introns, spacers).
  No possible selective pressure, faster rates of
  evolution

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Phylogenetics and Field Botany

• As molecular phylogenies replace those based on
  morphology, the traits used to establish the
  phylogenies may not be easily scored in the field
  and artificial keys may be more useful
  (especially at the subgenus level)
• For example, essential all taxonomic keys for
  the identification of North American sedges
  (Carex) break the genus up into 71 sections

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Plant Taxonomy Species concept

• Species the fundamental unit of plant
  classification
• Biological definition groups of actually or
  potentially interbreeding populations that are
  reproductively isolated from other groups
• Morphological definition groups of organisms
  sharing a conserved set of morphological traits
• Evolutionary definition populations that have
  diverged sufficiently from one another throughout
  evolution to be considered distinct lineages.

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Species concept in plants

• Species have traditionally been defined based on
  their morphological characteristics.
• However, many plant species interbreeding is
  possible and the hybrid offspring are fertile.
  Under field conditions interbreeding may be
  largely prevented by differences in geographic
  range, habitat, phenology (flowering time), or
  pollination mechanism.
• Hybrid swarms hybrid populations occurring
  where species ranges overlap. May be
  misidentified as separate species (Populus
  canescens)

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Problems with common names

• May convey misleading information concerning
  phylogenetic relationships (poison oak)
• Multiple species may share the same common name
  (bluebells, Indian paintbrush, etc.)
• Common names may vary between geographic regions

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Species names Polynomial System

• Developed by herbalists of the middle ages
• Each species is assigned a polynomial Latin
  name. The first word being the genus name (noun),
  following by strings of descriptive words
• Mentha floribus spicatis, foliis oblongis
  serratis
• Translation - Mentha (mint) with flowers in a
  spike, leaves oblong and serrated

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Species names Binomial System

• Binomial system originated with the publication
  of Species Plantarum by Linnaeus in 1753
• Each species assigned a standard polynomial and
  a a two word name (binomial), that was used in
  the margins to facilitate indexing and
  referencing.
• Mentha floribus spicatis, foliis oblongis
  serratis
• Mentha spicata

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Species names Binomial System

• Additional conventions (established since
  Linneaus)
• - Genus name capitalized, specific epithet in
  lowercase letters, both italized. The specific
  epithet an adjective or personal noun.
• - Latin words used for both names. Why?
• - The specific epithet typically followed by an
  abbreviation indicating the species authority
  i.e., L - Linnaeus.
• Quercus alba L. White oak
• Carex grayii Carey - Common Bur Sedge
• Laportea canadensis (L.) Wedd. Wood nettle

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Species documentation

• Type specimens herbarium specimens collected
  in association with the identification of new
  species and the assigning of binomial names
• Holotypes the reference specimen designated by
  the species authority
• Isotypes duplicates of the holotype in other
  herbaria, gathered at the same time as the
  holotype from the same plant or same population

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Other types of type specimens

• Lectotype a specimen or illustration
  designated as the type when no holotype was
  indicated at the time or publication
• Syntype anyone of two or more specimens
  referenced by the author when no single type
  specimen (holotype ) was designated
• Neotype a specimen or illustration selected a
  the type when all of the material on which the
  name of the taxon was based is missing

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Naming of hybrids

• Interspecific hybrids
• Cross Abelia chinensis x A. uniflora
• Name Abelia X gradiflora
• Intergeneric hybrids
• Cross Cupressus macrocarpa x Chamaecyparis
  nootkatensis
• Name X Cupressocyparis leylandii
• New genus name and specific epithet

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Organization into higher order taxaLinnaeus

• - Over 1300 plant species described
• - Organized into 24 classes
• 1) Non-flowering plants (all grouped together)
• 2) 23 classes of flowering plants based on
  stamen characteristics (number of stamens per
  flower, stamen morphology, relationship to other
  flower parts, etc.

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Organization into higher order taxaEichler,
Engler and Prantl (Late 1800s)

• Division (Phyla) - phyta (More Inclusive)
• Subdivision - phytina
• Class - opsida
• Subclass - idae
• Order - ales
• Suborder - ineae
• Family - aceae
• Subfamily - oideae
• Tribe - eae
• Subtribe - inae
• Genus - none
• Sections - none (More Exclusive)

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Higher order taxa Red cedar

• Juniperus virginiana L.   
• KingdomPlantae Plants       
• SubkingdomTracheobionta Vascular plants
           
• SuperdivisionSpermatophyta Seed plants
              
• DivisionConiferophyta Conifers                
  
• ClassPinopsida                   
• OrderPinales                      
• FamilyCupressaceae Cypress family
                          
• GenusJuniperus L. juniper                      
        
• SpeciesJuniperus virginiana L. eastern redcedar

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Higher order taxa Corn

• Zea mays L.    
• KingdomPlantae Plants       
• SubkingdomTracheobionta Vascular plants
           
• SuperdivisionSpermatophyta Seed plants
              
• DivisionMagnoliophyta Flowering plants
                 
• ClassLiliopsida Monocotyledons
                    
• SubclassCommelinidae                      
• OrderCyperales                         
• FamilyPoaceae Grass family                     
         
• GenusZea L. corn                               
  
• SpeciesZea mays L. corn

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Plant Divisions Non-vascular plants

• Division Common Name Species
•     
• Hepatophyta Liverworts 6,000
• Anthocerophyta Hornworts 100
• Bryophyta Mosses 10,000

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Plant Divisions Vascular Seedless Plants

• Division Common Name Species
•     
• Psilotophyta Wisk ferns 140
• Lycophyta Club mosses 1000
• Sphenophyta Horsetails 15
• Pteridophyta True ferns 12,000

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Plant Divisions Seed Plants

• Division Common Name Species
•     
• Cycadophyta Cycads 140
• Ginkgophyta Ginkgos 1
• Gentophyta 70
• Coniferophyta Conifers 550
• Anthophyta Flowering Plants 240,000
• Sometimes also termed the Magnoliophyta

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Classes of Flowering Plants

• Magnoliopsida (Dicots) 175,000 species
• Liliopsida (Monocots) 65,000 species

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Classes of Flowering Plants

• Monocots Dicots
• Floral Organs Trimerous Fours or Fives
• Venation Parallel Reticulate
• Secondary Growth Absent Present
• Vascular bundles (stem) Scattered In cylinder
• Number of cotyledons One Two

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Classification Below the Species Level

• Varieties - a naturally occurring variant of a
  species that is significantly different from the
  general species in one or more ways, such as in
  color size, shape, chemical quality, etc. The
  characteristics of varieties are typically fairly
  highly conserved through seed reproduction.
  Sassafras albidum var. molle
• Forms the lowest subdivision of a species
  ranking, reserved for minor variances such as
  differences in flower or fruit color. Forms are
  frequently defined based on differences in a
  single trait. However, these differences are
  typically heritable. Not a recognized category
  by the ICBN (International Code of Botanical
  Nomenclature)
• Cultivars - a cultivated variety i.e., plants
  exhibiting one or more distinctive features, in
  addition to those that are characteristic of the
  species,. Cultivars may originate as mutations
  or as a result of cross breeding. Most do not
  reproduce purely from seed. Examples Acer rubrum
  October Glory, Acer rubrum cv. October glory

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Plant Names through Time

• Plant names change through time as a consequence
  of changes in our understanding of plant
  phylogeny and as a result of differences in
  opinion about the degree of difference that is
  necessary to confer genus or species status
• Examples
• - New genera or species created (splitters)
• - Genera or species combined (lumpers)
• - Movement between genera or other taxa
  (phylogenetic revision)

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Documenting changes in species names

• The name (abbreviation) of the original author is
  indicated in parenthesis before the name of the
  author assigning the new name.
• Examples
• Taxodium distichum (L.) Rich
• Originally classified as Cupressus distichum
  by Linnaeus, but when the new genus Taxodium
  (bald cypress) was created the species was moved
  to this genus.