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Announcements

  • Midterm 2: One week from today. Resources have been posted for study.

  • Study Materials:

    • Study questions and key uploaded by Professor Keane.

    • Plants study guide and practice exam also available.

    • Recommended to work through the materials, especially the large plant phylogeny exercise in the study guide.

Key Characteristics of Euphyllophytes

  • Definition: Euphyllophytes include manilophytes (ferns) and seed plants.

  • Distinct Features:

    • Presence of megaphylls (large vascularized leaves).

    • Overtopping growth.

    • DNA chloroplast inversion: A unique evolutionary occurrence with no known function.

  • Comparison of Leaf Types:

    • Megaphylls: Evolved through overtopping, planation, and filling in with photosynthetic tissue.

    • Microphylls: Found in lycophytes and evolved from sterilized sporangia.

  • Importance of Distinction: Megaphylls and microphylls are not homologous structures, meaning they evolved independently.

Manilophytes (Ferns)

  • Diversity: Over 12,000 species with a well-preserved fossil record.

  • Structure:

    • Rhizome: The underground stem from which roots grow.

    • Sporangia clusters (sori) found on leaf undersurfaces.

    • Leaf development: Characteristic unfurling pattern known as fiddleheads.

  • Safety Note: Many fern species can be toxic if ingested.

Comparison of Life Cycles: Moss vs. Fern

  • Moss: The sporophyte is smaller and dependent on gametophyte.

  • Fern: The sporophyte is larger and dominates the life cycle.

Other Groups within Ferns

  • Equisetum (Horsetails):

    • Characteristics: Hollow stems, growth in riparian areas.

    • Structures: Produce cones (strobili) instead of sori.

    • Modified Leaves: Small structures, not functional leaves.

  • Whisk Ferns:

    • Features: Dichotomous branching, lack of sori.

    • Stubs called microphylls, misleadingly named; they evolved from megaphylls.

Seed Plants

  • Definition: Include key innovations like seeds and pollen, vital for reproduction.

  • Fossil Groups:

    • Progymnosperms: Woody plants without seeds.

    • Seed ferns: Early seed producers not aligned with true ferns.

  • Evolutionary Context:

    • Order of Evolution: Wood first, then seeds.

Synapomorphies of Seed Plants

  • Common Traits:

    • Seeds, pollen, heterospori, and secondary growth.

  • Reduction of Gametophytes: Trend towards smaller gametophytes in evolution.

Structure of Seeds and Pollen

  • Seeds:

    • Components: Embryo, seed coat, nutritive tissue (different in gymnosperms and angiosperms).

  • Pollen:

    • Function: Delivers sperm directly to the egg, freeing plants from water dependence during fertilization.

    • Structure: Tough outer coating enables fossilization and survival for long periods.

Differences Between Gymnosperms and Angiosperms

  • Gymnosperms: Do not produce fruit.

  • Angiosperms: Fruits develop as ripened ovary walls, containing seeds.

Mechanisms of Seed Dispersal

  • Seeds can be dispersed through wind, water, or animals, enhancing plant reproduction and survival.

Conclusion

  • Understanding plant evolution, particularly the development of seeds and pollen, is crucial for comprehending plant biodiversity.

Q&A Session

  • Encouraged discussion among peers to clarify key concepts and prepare for the upcoming exam.