Plant Lineage Study Notes

PLANTAE LINEAGE

PLANTAE LINEAGE OVERVIEW

  • Key Topics of Discussion:

    • Plantae Synapomorphies

    • Plantae Phylogeny

    • Red & Green Algae

    • Land Plants

      • Importance

      • Life Cycle

      • Adaptations to Land

      • Vascular Plants

      • Seed Plants

MAJOR LINEAGES OF EUKARYA: PLANTAE

  • Characteristic Features:

    • Photosynthetic organisms

    • All subgroups descended from a common ancestor that engulfed a cyanobacterium

    • Includes red algae, green algae, and all terrestrial land plants

ENDOSYMBIOSIS IN PLANTAE

  • The origin of chloroplasts in Plantae can be attributed to endosymbiosis:

    • The Plantae ancestor that engulfed the cyanobacterium did so via:

    1. Primary Endosymbiosis; this event created two membranes around chloroplasts.

    2. Alternative options for context:

      • Secondary Endosymbiosis; four membranes may indicate a different lineage.

      • Four membranes are observed in other contexts related to secondary endosymbiosis.

CLASSIFICATION OF PLANTAE AND OTHER EUKARYA GROUPS

  • Major Lineages:

    • Opisthokonta

    • Plantae

    • Alveolata

    • Stramenopila

    • Rhizaria

    • Excavata

    • Amoebozoa

  • Group characteristics:

    • Eukaryotic cells with specialized structures such as flagella with hair-like projections, alveoli, and pseudopodia.

PLANTAE TAXONOMY

  • Chloroplasts Characteristics:

    • Contain chlorophyll a and b, as well as β-carotene.

  • Major Groups:

    • Glaucophyta (glaucophyte algae)

    • Rhodophyta (red algae)

    • Green Plants:

      • Ulvophyceae (ulvophytes)

      • Charophyceae (stoneworts)

      • Coleochaetophyceae (coleochaetes)

      • Zygnematophyceae (conjugating algae)

    • Land Plants:

      • Nonvascular Plants:

        • Anthocerophyta (hornworts)

        • Bryophyta (mosses)

        • Hepaticophyta (liverworts)

      • Vascular Plants:

        • Seedless Plants:

          • Lycophyta (club mosses)

          • Psilotophyta (whisk ferns)

          • Pteridophyta (ferns)

        • Seed Plants:

          • Gymnosperms:

            • Ginkgophyta (ginkgoes)

            • Cycadophyta (cycads)

            • Cupressophyta (redwoods et al.)

            • Pinophyta (pines et al.)

            • Gnetophyta (gnetophytes)

          • Angiosperms (Flowering Plants):

            • Anthophyta (angiosperms)

SPECIES DIVERSITY OF LAND PLANTS (2016 DATA)

  • Distribution of land plant species:

    • Angiosperms: 250,000 species (89%)

    • Gymnosperms: 760 species (0.3%)

    • Ferns: 13,000 species (4%)

    • Mosses: 16,000 species (6%)

    • Other plants: 1,300 species (0.5%)

PLANT VOCABULARY ROOT WORDS

  • Different morphological and functional terms:

    • Phyte: Plant

    • Phyll: Leaf

    • Micro: Small/Male

    • Mega: Large/Female

    • Homo: Same

    • Hetero: Different

    • Angium: Container/Vessel

ALGAE: BASAL LINEAGES OF PLANTS

  • General Characteristics of Algae:

    • No true leaves, roots, or stems

    • Photosynthetic and supported by water

    • Tissues called a thallus; absorb all nutrients directly through tissues

RED AND GREEN ALGAE

  • Red Algae:

    • Multicellular, reflect red light due to pigments.

    • Nearly all are marine organisms.

  • Green Algae:

    • Can be single-celled or multicellular.

    • Contain chlorophylls A & B that reflect green light.

    • Commonly found in aquatic environments.

IMPORTANCE OF LAND PLANTS

  • Contributed to changing terrestrial ecosystems:

    • Land plants were the first multicellular organisms to thrive with tissues exposed to air.

    • They facilitated diversified life on land previously dominated by single-celled organisms (bacteria, archaea, and eukaryotes).

ROLE OF PLANTS IN ECOSYSTEMS

  • Key ecological roles:

    • Fix carbon from CO₂ into glucose.

    • Foundational source of energy for other organisms within terrestrial ecosystems.

ALTERNATION OF GENERATIONS LIFE CYCLE

  1. Sporophyte: Produces haploid spores via meiosis.

  2. Spores: Divide by mitosis to develop into haploid gametophytes.

  3. Haploid Gametophytes: Produce haploid gametes by mitosis.

  4. Fertilization: Resulting diploid zygote undergoes mitosis to form a multicellular diploid sporophyte.

EXAMPLE: MOSSES

  • In mosses:

    • Gametophyte is the dominant stage, and it relies on the sporophyte for nutrients.

    • The lifecycle stages clearly differentiate between haploid and diploid phases with specific gametangia:

      • Sperm in antheridia and eggs in archegonia.

CHALLENGES AND BENEFITS OF MOVING TO LAND

  • Benefits:

    • Increased light energy availability

    • Higher CO₂ concentration in the atmosphere

    • Access to more mineral nutrients

    • Fewer herbivores/pathogens present

    • More ecological niches to explore

  • Challenges:

    • Water loss management

    • UV radiation exposure

    • Gas exchange mechanisms

    • Structural support in upright growth without water column support

    • Transportation of water to various tissues

    • Reproduction without the aid of water

MAJOR OBSTACLES TO LIFE ON LAND

  1. Control water loss

  2. Survive intense sunlight

  3. Grow upright against gravity

  4. Reproduce without water

  5. Effective movement capabilities

ADAPTATIONS TO PREVENT WATER LOSS

  • Cuticle:

    • A waxy layer on stems and leaves that minimizes water loss from surfaces.

  • Stomata:

    • Pores that allow gas exchange while controlling water loss.

    • Guard Cells: Control the opening and closing of stomata, facilitating gas exchange while minimizing desiccation.

UV PROTECTION IN PLANTS

  • Flavonoids:

    • Compounds that protect plant DNA from ultraviolet radiation and other sun damage.

    • Additionally serve as pigments in flowering plant petals.

FIRST LAND PLANTS: MOSSES

  • Key Reduced Structures:

    • Gametophyte is dominant, capable of absorbing water and CO₂ through surface cells.

    • Lack of vascular tissue limits size and structure, resulting in reliance on moist environments.

REPRODUCTION UNDER DRY CONDITIONS

  • Sporopollenin:

    • A tough coating on spores that enables resistance to desiccation.

    • Spores can endure long periods and travel significant distances via wind.

STRATEGIES BY MOSSES TO ADDRESS LAND CHALLENGES

  1. Control water loss via cuticles and necessitating proximity to water

  2. Protect against intense sunlight via flavonoid compounds

  3. Structural limitations prevent upright growth

  4. Reproduce in moist environments where sperm can swim to eggs

  5. Utilize wind for spore dispersion

TEST QUESTIONS

  • Which structures evolved to prevent excessive water loss?

    • Options include stomata, flavonoids, cuticle, gametophyte dominance, vascular tissue.

FINAL THOUGHT

  • The evolutionary history of the Plantae lineage demonstrates a remarkable transition from water to land, shaping terrestrial life as we understand it today.

  • Understanding plant life cycles, adaptations, and ecological contributions is crucial for appreciating biodiversity and ecosystem functioning.