Plant Taxonomy

Taxonomy is the science of describing, naming and classifying organisms. 
Classification is arranging organisms into groups based on their similarities. 
Systematic is the classification of plants and other organisms into groups determined by their evolutionary relationship. It is also the scientific study of the diversity of organisms and their natural relationships.


The hierarchical grouping of classification:

• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Six Kingdom of life:

1. Bacteria
2. Archaea
3. Protista
4. Fungi (Myceteae)
5. Plantae
6. Animalia 

1. Bacteria
Some important bacteria:

1. Nitrogen-fixing bacteria, they fix nitrogen, can be free-living (Azotobacter, Derxia) or form symbotic relationships with plants (Agrobacterium, Rhizabium)
2. Nitrifying bacteria, Nitrosomonas and Nitrosococcus oxidize ammonium to nitrite, and Nitrobacter and Nitrococcus further oxidize the nitrite to nitrate. 
3. Denitrifying bacteria (Hyphomicrobium), they reduce nitrate to gaseous nitrogen. 
4. Cynobacteria or blue-green bacteria (such as Anabaena)-photosynthetic autotrophs. Cynobacteria are the only organisms that can both fix nitrogen and produce oxygen.

2. Archaea
The Archaea are divided into three groups on the basis of habitat:

1. Methanogens - Most common archaea that produce methane gas from simple carbon compound They inhabit sewage and swamp sediments and are common in the digestive tracts of humans and other animals. 
2. Halophiles - The salt bacteri. Extreme halophiles live in very salty environment (e.g. salt ponds, Dead Sea, Great Salt Lake); use aerobic respiration, carry out photosynthesis by using a purple pigment to capture the energy of sunlight. E.g Halobacterium, found in salt pools.
3. Thermophiles - The Sulfolobus bacteria. Live in hot (45-110 degree Celsius), acidic environments such as sulfur hotspring, anaerobic (do no need oxygen to live, some may be poisoned by oxygen).

3. Protista
Some live in fresh water or salt water, some live on land, diatoms (planktons) are the most abundant organism in the ocean, some have chlorophyll c instead of chlorophyll b, can reproduce asexually or sexually. Green algae give rise to members of the plant kingdom.
Protista examples:

• Euglenoids
• Dinoflagellates
• Diatoms
• Golden brown algae
• Yellow-green algae
• Green algae
• Red algae

4. Fungi (Myceteae)
They can be classified into 3 groups based on modes of nutrition:

1.  Biotroph gets nutrients from other living thing organisms, without killing them
2.  Necrotroph attack living hosts virulently, killing the hosts and then absorbs released nutrients
3.  Saprotroph gets nutrients from dead organisms.

Some important fungi:

1. Yeast
2. Disease causing fungi e.g rust, downy mildew, damping-off, rot, powdery mildew in plants. 
3. Edible fungi
4. Mycorrhizae

5. Plantae
 Non-vascular plants:

1. Mosses
   - Antheridum: A multicellular male gametangium that produces sperm cells.
   - Archegonium: A multicellular female gametangium that produces an egg
2. Liverworts
3. Hornworts

Vascular plants
We can classify vascular plants into two main groups: 1) Plants without seed 2) Plants with seeds.

1) Plants without seed (spore-bearing, non-flowering plants) : 

1. Psilotum
2. Lycopodium
3. Equisetum
4. Ferns

2) Plants with seeds:

1. Gymnosperms (cone-bearing, non-flowering naked seed e.g pines, have male cones and female cones, no  flowers)
   
   •  Coniferophyta
   • Cycadophyta
   • Ginkgophyta
   • Gnetophyta
2. Angiosperms (flowering plants, dicots and monocots)
   • Anthophyta / Magnoliophyta:
     Includes all the monocots and dicots, also known as angiosperms, their seeds are enclosed by carpels. They have flowers. Vessels are found in the wood.
   • Monocots:
     
     • One of the main classes of flowering plants.
     • Monocot seeds contains one seed leaf (single cotyledon).
     • Usually have parallel leaf venation
     • Flower parts usually occur in multiples of threes e.g three sepals, three petals, three stamens.
     • e.g of plants includes grasses, orchids, palms
   
   
   • Dicots:
     
     • One of the main classes of flowering plants. 
     •  Dicot seeds contains two seed leaves (two cotyledon). 
     • Net leaf venation
     •  Flower parts usually occur in multiples of four or five

Taxonomy

Theophrastus was a Greek philosopher and biologist who classified several hundred plants into groups such as herbs, shrubs and trees.

Dioscorides was a Roman military surgeon on Roman army who wrote Materia Medica (600 species of medicinal plants) and has provided medical reference for ~1500 years.

Carolus Linnaeus was a Swedish botanists who  designed classification system in mid- 18th century, has survived, with some modification, to the present day. He published Species Plantarum in 1753 of which described 7300 species, classified based on observation.

Scholars used Latin sentences up to 12 words long to describe each type of plant.
E.g spearmint: Genus: Mentha

Mentha spicata
Latin: Mentha floribus spicatis follis oblongis serratis
Translated: Mentha with flowers in a spike; leaves oblong, saw-toothed
Single word: spicata

These abbreviated name became known as binomials. The system of naming is known as Binomial System of Nomenclature

Binomial System of Nomenclature

• A system for giving each organism a two-word scientific name

Corn: Zea mays

Corn- Common name
Zea- Genus name (Starts with capital letter)
may- Species name (Starts with small letter)

*Always remember to underline or italicize scientific names else you will get deducted marks during exam! :P

• Genus name can be used alone to designate all species in the genus.
• Specific epithet, designate the species, usually a word that describe some particular quality of the organism, never used alone, always preceded by the full or abbreviated generic name. 
• Specific epithet can be used in more than one genus. 

Citation of Author's name

• A complete botanical/scientific name for a particular plant must be followed by the name of the person who have identified and described the plant. E.g Sesamum indicum named by Linnaeus
  Sesamum indicum L. 
  

International Code of Botanical Nomenclature (ICBN)

Six principles:

• Principle 1:
  Botanical nomenclature is independent of zoological nomenclature
  (i.e it is possible to have same name for two quite different organisms)

• Principle 2:
  The application of names of taxonomic groups is determined by means of nomenclature types.(Types: The name used for a particular plant or group is based on one particular specimen, the type specimen stored in a dried-plant repository called herbarium.)
  
  
  • Holotype is the one specimen or other element used or designated by the author in the original publication as the main nomenclature
  • Isotype
  • Syntype
  • Paratype
  • Lectotype or neotype

• Principle 3:
  The nomenclature of a taxonomic group is based upon "Priority of Publication".
  (each taxon should bear only one correct name and that should be he earliest published names.)

• Principle 4:
  Each taxonomic group with a particular circumscription, position, and rank can bear only one correct name, that is a validly and effectively published name.
  (each taxon should bear only one correct name and that should be the earliest published name.)

• Principle 5:
  Scientific names of taxonomic groups are treated as Latin regardless of their derivation.
  e.g A plant named after Ferdinand Mueller is called, for example, not Eucalyptus mueller but Eucalyptus muelleriana where the name is given a standard Latin suffix. 

• Principle 6:
  The rules of nomenclature are retroactive unless expressly limited.

Ranks and Taxa

Most commonly referred to ranks are Family, Genus and Species.

Taxonomic level

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species
  
  • Subspecies
  • Varieties
  • Cultivar

Genus

• The genus name represents a group of plants with similar characteristics

• In evolutionary terms the genus name represents a common ancestor of all the plants contained in the genus 

Species

• The species is the basic unit of classification.
• It represent a sub-group of one or more plants within the genus; with similar characteristic. 

Subspecies

• Geographically distinct population within a species that evolves by natural selection
• Display certain characteristic that distinguish them from other population of the same species. 
• If they can interbreed, they are not truly separate species but are known as subspecies. 

Variety

• Within a species there can be minor characteristics that differ from the usual characteristics of the species. 
• The variations can occur either naturally through cross fertilization of plants or deliberate breeding of plants.
• These characters do not have a clearly defined geographical or ecological distribution.
• A naturally occurring variety is referred to as variety.
• A bred variety is referred to as cultivar (cultivated variety).
  E.g Eucalyptus ovata var. grandiflora

Cultivars

• Plants that are produced using techniques such as selective breeding, in an effort to produce a better or more attractive varieties. 
• Cultivar is an abbreviated form of cultivated variety. 
• The cultivar name will be chosen by the breeder and will therefore be in the native language.
  
  • Bougainvillea glabra 'Singapore Pink'
  • Papaver orientalis 'Mrs Perry'

Hybrid

• Hybrids result from the sexual reproduction or interbreeding between different varieties, species or genera.
• It mostly of related species, almost always in the same genus.
• E.g Eucalyptus camaldulensis x E.ovata
• Hybrid between two different species has an 'x' placed in front of the species name
  
  • Magnolia x soulangiana
• Hybrid between two different genera has an 'x' placed in front of the genus name, e.g
  
  • Osmaria burkwoodii