Plant Systematics and Evolution: Comprehensive Study Notes

PLANTS

  • Definition of a plant (Page 2):
    • A. To define groups of organisms such as plants by the characteristics they possess. Plant-related criteria include photosynthesis, cell walls, spores, and a predominantly sedentary lifestyle.
    • B. To evaluate the evolutionary history of life and to use that history to delimit the groups of life.

PLANTS AND THE EVOLUTION OF LIFE

  • Three major groups (domains) of organisms:
    • 1) Archaea (also called Archaebacteria)
    • 2) Bacteria (also called Eubacteria)
    • 3) Eukarya or Eukaryotes
  • Evolutionary relationships summarized in the evolutionary tree or cladogram (Figure on slide 4).

EVOLUTIONARY RELATIONSHIPS AND ENDOSYMBIOSIS

  • Diagram and major components (as described on Page 4):
    • Bacteria, Archaea, Euglenoids, Amoeboids/flagellates, Alveolates, dinoflagellates, ciliates, sporozoans, oomycota (water molds), brown algae, red algae, green plants (Chlorobionta), fungi, animalia, secondary endosymbiosis hints, and chloroplast evolution terms.
    • Chloroplast origin is linked to endosymbiotic events; primary endosymbiosis is the origin of chloroplasts from ancestral cyanobacteria, with/without secondary events affecting chloroplasts.
    • Mitochondria also originated by endosymbiosis, along with other organelles.
  • Key concepts:
    • Endosymbiosis: one cell living inside another in a symbiotic relationship; endosymbiosis refers to engulfment events leading to organelle origin.
    • Primary Endosymbiosis: chloroplasts originate from an engulfed photosynthetic bacterium.
    • Secondary Endosymbiosis: chloroplasts (or derived features) arise via subsequent engulfment events.
    • Evidence for endosymbiosis in chloroplasts and mitochondria:
    • Chloroplasts have their own circular DNA, similar to bacteria.
    • Chloroplasts have a 70S ribosome, smaller size compared to cytosolic ribosomes.
    • Chloroplasts replicate by fission.
    • Host cell provides a favorable environment for the endosymbiont; the endosymbiont provides high-energy products.
  • Terminology:
    • Symbiosis: two species living together in close contact.
    • Endosymbiosis: engulfment of one cell by another leading to long-term symbiotic association.

LAND PLANTS

  • The green plants (Chlorobionta) are united by distinctive chloroplast characteristics (pigments, thylakoid structure, storage compounds).
  • Green plants include:
    • Predominantly aquatic green algae
    • Embryophytes (embryophyta), i.e., land plants

LAND PLANTS (Key features)

  • (1) Outer cuticle to reduce desiccation risk in terrestrial environments.
  • (2) Specialized gametangia (egg and sperm producing organs) with an outer protective layer of sterile cells.
  • (3) A diploid phase in the life cycle that includes an embryo (intercalated diploid phase).

WHY STUDY PLANTS?

  • First reason: Photosynthesis altered Earth's atmosphere by fixing CO₂ and releasing O₂ over billions of years.
    • Result: Oxygen-rich atmosphere enabled the formation of the ozone layer, shielding life from excess UV radiation and allowing life in exposed niches.
  • Second reason: Photosynthetic products feed nonphotosynthetic organisms.
    • Land plants are primary producers in many ecosystems, forming the base of food chains.
    • Their survival supports ecosystem health; disruption can lead to extirpation/extinction, erosion, altered water flow, and climate impact.

THE PEOPLE, METHODS AND RATIONALE OF THE PLANT SCIENCES

  • The scope of plant sciences includes land plants; fields include:
    • a. Agriculture and horticulture: improving crop yield and disease resistance of food crops and ornamental plants.
    • b. Forestry: cultivation and harvesting of trees for lumber and pulp.
    • c. Pharmacognosy: crude natural drugs, often of plant origin.

PURE SCIENCES IN PLANT BIOLOGY

  • Pure sciences aim to advance knowledge about how nature works, regardless of practical applications. Areas include:
    • a. Plant anatomy: cell and tissue structure and development.
    • b. Plant chemistry and physiology: biochemical and biophysical processes and products.
    • c. Plant molecular biology: structure and function of genetic material.
    • d. Plant ecology: interactions of plants with their environment; and plant systematics.

BOTANY VS. PLANT SCIENCES

  • Distinction:
    • Plant sciences: study of plants (land plants primarily).
    • Botany: broader, includes virtually all eukaryotic photosynthetic organisms (land plants and some algae) plus other eukaryotic organisms with cell walls and spores (true fungi and groups formerly treated as fungi, e.g., Oomycota and slime molds).

SYSTEMATICS

  • Systematics is a science that includes and encompasses traditional taxonomy (description, identification, nomenclature, and classification) with the primary goal of reconstructing phylogeny (the evolutionary history of life).
  • Plant systematics involves acquiring, analyzing, and synthesizing information about plants and plant parts.
  • Systematics is founded on the principles of evolution; the major premise is that there is one phylogeny of life, and the goal is to discover that phylogeny.

EVOLUTION (General)

  • Broad sense: evolution means change; cumulative changes since the origin of the universe (~$15$ billion years ago).
  • Biological evolution: descent with modification.
    • Descent: transfer of genetic material from parents to offspring over time.
    • All life is derived from preexisting life.
    • Descent through time forms a lineage or clade (interconnected populations through time and space).

EVOLUTION: MODIFICATION

  • Modification component: changes in genetic material transmitted from parents to offspring, resulting in offspring with different genetic material from parents.
  • Modification can occur via mutation or genetic recombination.
  • Systematics identifies the unique modifications of evolution.

EVOLUTION: UNITS AND DEFINITIONS

  • General units of evolution: populations and species.
  • Population: group of individuals of the same species, usually geographically delimited, with significant gene exchange.
  • Species: can be defined in several ways; one definition is a distinct lineage of sexually reproducing organisms consisting of intergrading, interbreeding populations that are reproductively isolated from other such groups.

EVOLUTION: MECHANISMS

  • Two major mechanisms drive evolutionary change:
    • (1) Genetic drift: random genetic modification.
    • (2) Natural selection: nonrandom, directional genetic change across generations.
  • Natural selection results in differential contributions to the next generation; fitness is the quantitative measure of this differential contribution.

EVOLUTION: ADAPTATION AND SPECIATION

  • Natural selection leads to adaptation: a structure/feature that performs a function and increases survival or reproduction.
  • Speciation: formation of new species from preexisting species.
    • Can follow lineage divergence: splitting of one lineage into two separate lineages.

TAXONOMY

  • Taxonomy is a major part of systematics and includes four components (often abbreviated D I N C):
    • Description: assignment of features/attributes to a taxon; features are called characters; variation in a character is called character states.
    • Identification: determining the identity of an unknown taxon by comparing to known taxa; may involve discovering a new species requiring formal description and naming.
    • Nomenclature: formal naming of taxa according to a standardized system; names are Latinized (scientific names).
    • Classification: arranging entities into a hierarchical order using taxonomic ranks.

TAXONOMY: IDENTIFICATION DEVICES AND NOMENCLATURE

  • A taxonomic key is widely used for identification.
  • Dichotomous key: most common; consists of a series of two contrasting statements (couplets).
  • Process: choose the couplet whose lead best fits the specimen; follow hierarchical leads until an identification is reached.

TAXONOMY: NOMENCLATURE AND RANKS

  • Nomenclature: formal naming of taxa; uses scientific names, Latinized.
  • Fundamental principle: every taxon bears only one scientific name.
  • Species names use binomial nomenclature (two names).
  • Historical note: binomial nomenclature was first formalized in the mid-18th century by __.
  • Classification uses ranks; two major methods to classify life:
    • a. Phenetic: based on overall similarities.
    • b. Phylogenetic: based on evolutionary history or pattern of descent; may or may not correspond to overall similarity.

PHYLOGENY

  • Phylogeny: the evolutionary history of a group of organisms; primary goal of systematics.
  • Representation: cladogram (phylogenetic tree), a branching diagram representing descent.
  • Lines in a cladogram denote lineages or clades; the sequence of ancestral-descendant populations through time.
  • Branching events represent lineage divergence from a common ancestor.

PHYLOGENY: DERIVING AND APOMORPHY

  • Changes in genetic makeup over time can be traced in lineages.
  • Evolution may be seen as a change from ancestral character state to a derived character state.
  • Derived state: evolutionary novelty, also called an apomorphy.

PHYLOGENY: PHYLOGENETIC SYSTEMATICS ( cladistics )

  • Phylogenetic systematics (cladistics): methodology for inferring evolutionary history using apomorphies.
  • Monophyletic group: includes a common ancestor and all (and only all) descendants of that ancestor.
  • Paraphyletic group: includes a common ancestor and some, but not all, descendants.
  • Polyphyletic group: composed of two or more groups with separate common ancestors.

ACTIVITY

  • Task: Answer the question below, prepare in MS Word, convert to PDF, and turn in by 5 PM today.
  • Essay format, 3–5 paragraphs.
  • QUESTION: WHY STUDY SYSTEMATICS?