Chapter 1: Organisation of the Living World PDF

# Chapter 1: Organisation of the Living World ## 1 - Taxonomy and Systematics The study of the plant world requires knowledge of the classification of plants. Systematics is the scientific study of biological diversity and its evolutionary history. Taxonomy (Taxinomie) consists of identifying, nam...

# Chapter 1: Organisation of the Living World ## 1 - Taxonomy and Systematics The study of the plant world requires knowledge of the classification of plants. Systematics is the scientific study of biological diversity and its evolutionary history. Taxonomy (Taxinomie) consists of identifying, naming, and classifying living organisms into groups that are as homogeneous as possible. In most disciplines of life sciences, the term taxonomy is inseparable from that of systematics. **Species** is the basic systematic unit in botanical nomenclature. It defines a group of individuals that resemble each other morphologically and are capable of reproducing among themselves. ## Classification The classification of biology began with the Swedish botanist Carl Von Linné (1753), who invented the **binomial nomenclature** system. Each plant (or organism) has a **scientific Latin name** recognized by an international botanical nomenclature code (CINB) that identifies it with precision throughout the world. According to the rules of this code, the name of the species is designated by a double (binomial Latin) name: the **genus name** (or generic name common to several species), followed by the **specific epithet** (specific name) and accompanied by the initial or abbreviation of the botanist who described this species. The names of genera and specific epithets are written in italics or underlined; the first is capitalized, the second in lowercase. Its French name is called the **vernacular name** or **common name**. **Examples:** * *Pinus sylvestris* L. or Scots pine (vernacular name) described by Linné * *Pinus maritima* Lam. or maritime pine described by Lamarck Genus names can be written alone to refer to the set of species that make up a genus. ## Subdivisions A species can be subdivided into two or more subspecies, races, varieties, or forms that share the same essential characteristics and differ only in minor ways (color, hairiness, etc.). Following the same classification principle, several shared traits group species into genera, genera into families, families into orders, orders into classes, and classes into **phyla** or **divisions**. The set of all plant divisions makes up the **plant kingdom**. Each level of this classification is called a **taxon** (plural taxa). The main taxa, presented in descending order, are: * Kingdom * Phylum or division * Class * Order * Family * Genus * Species - **Family names** end in -aceae. - **Order names** end in -ales. - **Class names** end in -psida. - **Phylum names** end in -phyta. Botanical nomenclature recommends using italics for all taxonomic names, not just genus and species names. ## 2 - Diverse Classifications ### 2.1 - Old Classifications Linné classified all living things into two kingdoms: **Animals** and **Plants**. * Fungi, Algae, and bacteria (Procaryotes) are organisms that cannot move or eat, so they were grouped within the plant kingdom. * Protozoans, which are unicellular organisms that can eat and move, are grouped among animals. This old division between animals and plants is still used today. In this 2-kingdom taxonomic system, some microorganisms, such as Euglena, which can move but can perform photosynthesis, were classified in both the plant and animal kingdoms. After Linne, Jussieu (1789) and De Candolle (1788-1841) expanded the classification of plants based on morphology: * **Acotyledones** (no embryo) * **Monocotyledones** (one cotyledon) * **Dicotyledones** (two cotyledons) They also considered important characters, such as the embryo, stamens, pistils, or floral envelopes, to determine new families. All known species were classified into those new families. Darwin (1859), after publishing work about the origin of species and Lamarck, grouped species based on their phylogeny. * **Phylogeny** is the evolutionary history of a group. * **Phylogenetic trees** represent the phylogeny of a group. * In a **phylogenetic** or **cladistic** system, every taxon should be **monophyletic** (clade). * A clade includes organisms that descended from a common ancestor, as well as all of its descendants. ### 2.2 - Modern Classifications Modern classifications rely heavily on biochemistry, especially on the synthesis of secondary metabolites and more recently on molecular biology. Molecular biology analysis include sequencing of amino acids in proteins and nucleotides in nucleic acids. **Robert H. Whittaker** (1969) and later **Margulis** (1981) divided the living world into five kingdoms: * **Procaryotes** and **Eucaryotes** are differentiated by how their cells are organized. - **Procaryotes** * unicellular, usually microscopic * lack true nuclei and organelles (mitochondria and plastids) * all belong to the **Monera** kingdom - **Eucaryotes** * mostly multicellular * contain organized, usually larger cells that have nuclei and organelles * include 4 kingdoms: **Protista**, **Fungi**, **Plantae**, and **Animalia**. ## 3 - Traditional Classification of the Plant Kingdom Traditional classification of the plant kingdom is still widely used, even after evolution of the classification. **Procaryotes** * **Schizophytes** - Bactéries - Cyanobactéries - Algues - Champignons - Lichens * **Thallophytes** - Bryophytes - Pteridophytes **Eucaryotes** * **Cormophytes** - Rhizophytes - Spermaphytes - Gymnospermes - Angiospermes * **Archégoniates** - Phanérogames ## 4 - Main Divisions of the Plant Kingdom * **Thallophytes** (thallos: sprout and phyton: plant) have a vegetative body called a thallus. * **Cormophytes** (cormos: trunk and phyton: plant) have shoots and a cormus. Cormophytes include Archegoniates (Bryophytes, Pteridophytes, and Gymnosperms) and Angiosperms. * The **Archegoniates** have a female reproductive organ called an archegonium. * **Cryptogames** (cryptos: hidden and gamos: marriage) are non-flowering and seedless plants including Algae, Fungi, Lichens, Bryophytes, and Pteridophytes * **Phanérogames** (phaneiros: obvious and gamos: marriage) are flowering and seed-producing plants. * **Spermaphytes** have seeds and include both Gymnosperms and Angiosperms. **Thallophytes** and **Bryophytes** are **non-vascular plants**, therefore they lack conductive tissue (xylem and phloem). **Pteridophytes** and **Spermaphytes** are **vascular plants**, so have conductive tissue and roots. ## 5 - Classification Issues * Some scientists include Fungi and Algae within the plant kingdom. * Others classify Fungi as a separate kingdom. * There is no single, universally accepted classification system. The classification of the plant kingdom varies from one book to another. This document describes only some of the major classifications of the living world. Understanding how organisms are classified will help you understand the evolutionary history of the plant world.