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Weed Biology and Identification-205 Target students: M.Sc. Students in Weed Science Lecture: Dr. Majid AghaAlikhani (Ph.D.) Academic position : Associate Prof. of Tarbiat Modares University email@example.com 1
Plant Taxonomy By: Johnny M. Jessup Agriculture Teacher/FFA Advisor
Introduction Taxonomy is the science of classifying and identifying plants. Scientific names are necessary because the same common name is used for different plants in different areas of the world. Latin is the language used for scientific classification.
Description Assignment/listing of features or attributes to a taxon character = a feature e.g., “flower color” character states = two or more forms of a character e.g., “white,” “red,” “yellow”
Identification Associating an unknown taxon with a known one How? taxonomic key compare to a photograph/illustration compare to a specimen ask an expert
Nomenclature Formal means of naming life. E.g., binomial nomenclature for species names: For Adenostoma fasciculatum Hook. & Arn. Adenostoma = genus name fasciculatum = specific epithet Adenostoma fasciculatum = species name Hooker & Arnott = authors of species name
Classification = placing objects, e.g., life, into some type of order. Taxon = a taxonomic group (plural = taxa).
How to classify life Phenetic classification Based on overall similarity Those organisms most similar to one another are classified more “closely” together.
Problem with phenetic class.: Can be arbitrary, e.g., classify these:
Definitions Taxonomy -- the naming of groups (taxa, singular taxon) Systematics -- a method (or system) for classifying organisms into groups Why classify?? Goals of Classification Simplify Communicate Predict
Functional classifications Based on function or overall similarity No assumption of evolutionary relationship
History - Functional classification systems All cultures classify plants in ways meaningful to them Examples of early plant classifications 2000 BC - Indian (Ayurvedic) texts described medicinal plants 1000-1700 AD - “Age of Herbals” in Europe
Botanical tradition Carolus Linneaus (Systemae naturae, 1732) - defined groups based on sexual characters - developed binomial system of plant nomenclature Engler, Bessey, Cronquist etc. (1800 - 1980s) - sought to define evolutionary groups of plants - published many regional floras (still in use) History - Evolutionary classification systems
Evolutionary classification (includes both traditional systematics and modern phylogenetics) 1.Living species are related to one another by descent from common ancestors 2.Shared character states are clues to relatedness Reasoning
Modern solution: Phylogenetic systematics Reconstructs relationships using lots of characters Now, primarily uses DNA sequence data From Nickrent et al.
Land plants (Embryophytes) Vascular plants ~450 million years ago Present Bryophytes (mosses, liverworts) Lycopods (club mosses) Seed plants Monophilites (ferns, horsetails) woodiness seeds tracheids (vascular cells for water transport) “true” leaves multiple adaptations to life on land
Karl von Linne (1707-1778) Swedish botanist Developed binomial classification scheme for plants. Uses two Latin words to indicate the genus and the species. Changed his name to the Latin name of Carolus Linnaeus.
Scientific Names The first word is the genus and the second word is the species. If there are additional words, they indicate the variety or cultivar.
Genus Plants in the same genus have similar characteristics. Examples: Quercus – Oaks Acer – Maples Pinus – Pines Ilex – Hollies Cornus – Dogwoods Ficus – Figs
Species Plants in the same species consistently produce plants of the same types.
Species A distinct types of organism capable of breeding with other members of its own kind - but not with other species…. Basic category in biological nomenclature
Varieties (subspecies) Sargent Quercus alba L. var. alba Quercus alba L. var. latiloba Sarg. If Q. latiloba was a new species? Quercus latiloba Sarg.
hybridization Q. velutina X Q. rubra X Q. palustris Echinacea pallida Echinacea paradoxa Echinacea pallida X paradoxa
Relationship between Genus and Species Genus - a group of related species Quercus (oaks)Carya (hickories) rubra- ovata velutina- cordiformes alba
Related 1. Have similar characteristics (may hybridize) 2. Have a common ancestor back in evolutionary time velutina rubra alba
Related 1. Have similar characteristics (may hybridize) 2. Have a common ancestor back in evolutionary time ovata cordiformes
Scientific Classification The broadest category of scientific classification is the Kingdom. Either Plant or Animal The broadest category of the plant kingdom is Division or Phylum.
Scientific Classification Kingdom Phylum/Division Class Order Suborder Family Genus Species
Natural System Our present system attempts to group organisms in accordance with natural (evolutionary) relationships. Homology internal structures, embryology, DNA, proteins Analogy based on superficial characteristics outward form and function
Rank Classification Hierarchical - each higher rank is inclusive of lower ranks RankExampleEnding PhylumMagnoliophyta-phyta ClassLiliopsida-opsida OrderLiliales-ales FamilyLiliaceae-aceae GenusLilium SpeciesLilium parryi
Divisions The four most important divisions of the plant kingdom are…. Thallophites Bryophytes Pteriophytes Spermatophytes
Includes flowering or seed-bearing plants. The two subdivisions are…. Gymnosperms Angiosperms
Kingdom Viridiplantae (green plants) Phylum/Division Embryophyta (land plants) Subphylum Tracheophytina (vascular plants) Class Angiospermopsida (angiosperms) Subclass Caryophyllidae Order Caryophyllales Family Portulacaceae (Purslane family) Genus Lewisia Species Lewisia rediviva Lewisia rediviva (Bitterroot) Plant nomenclature in practice
Higher ranks - Each rank has a characteristic ending (ex. -idae for subclasses, -ales for orders) - Ideally, all taxa are monophyletic, but ranks are arbitrary - In this class, we’ll focus on lower taxonomic levels --> subclass (ex. Rosidae vs. Asteridae) --> family (ex. Salicaceae vs. Betulaceae) --> genus (ex. Populus vs. Salix) --> species (ex. P. tremuloides vs. P. deltoides)
Plant nomenclature in practice ICBN (International Code of Botanical Nomenclature) Goal: Standardization of scientific names for plants - First adopted in 1903; includes fungi, lichens and algae Basic rules - Every taxon must have a type specimen - Names of higher ranks must be based on names of lower ones - Priority of publication determines “correct” name - Only 1 name is allowed per taxon, 1 taxon per name
Standard Endings (ICBN) Division: phyta Class: opsida Order: ales family: aceae Genus: species:
Plant nomenclature in practice Families - All end in -aceae (easiest to pronounce a-cee-ee) - Older alternate names also allowed for 8 families examples: Crucifereae = Brassicaceae (mustard family) Umbellifereae = Apiaceae (carrot family) Compositae = Asteraceae (sunflower family) - Always capitalize family names
Plant nomenclature in practice Species names (“scientific names”) are Latin binomials Lewisia rediviva Pursh. Genus (pl. genera) Always capitalized Abbreviated on 2 nd use (L. rediviva) Authority Specific epithet Not capitalized Often a descriptive adjective Always underline or italicize species names (genus + specific epithet)
Plant nomenclature in practice Why do names change? New evolutionary data Rediscovery of older names Lumpers vs. splitters Agropyron spicatum Elymus spicatus Psuedoroegneria spicata Bluebunch wheatgrass