28 Seedless Vascular Plants

Seedless Vascular Plants (Tracheophytes)

Learning Objectives

  • Identify new plant traits in seedless tracheophytes.

  • Discuss the significance of each trait for terrestrial life.

  • Identify various classes of seedless tracheophytes.

  • Describe the life cycle of a fern.

  • Explain the ecological role of seedless plants.

Overview of Tracheophytes

  • Definition: Vascular plants with over 260,000 species.

  • Dominant Structure: Diploid sporophyte stage is prevalent.

  • Fertilization: Seedless vascular plants require water (H2O).

Vascular Tissue

  • Originated approximately 430 million years ago.

  • Components:

    • Xylem: Responsible for the storage and long-distance transport of water.

      • Tracheids: Conducting cells that provide supportive filler tissue.

      • Incorporation of lignin gives structural rigidity.

    • Phloem: Transports sugars, proteins, and solutes throughout the plant.

      • Comprised of sieve elements (conducting cells) and supportive cells.

Parts of Seedless Vascular Plants

  • Roots:

    • Evolved post-vascular tissue development.

    • Functions: Absorb water/nutrients, anchor plants, and establish symbiotic relationships with fungi.

  • Leaves:

    • Microphylls (350 MYA): Single un-branched vein (xylem and phloem).

      • Example: Club mosses.

    • Megaphylls: Larger leaves with multiple veins.

  • Sporophylls and Strobili:

    • Sporophylls are modified to bear sporangia.

    • Strobili are cone-like structures containing sporangia (found in conifers).

Types of Seedless Vascular Plants

  • Dominance in Carboniferous Period (360-300 MYA)

  • Phylum Lycophyta (Club Mosses):

    • Earliest seedless vascular plants with 1,200 species today.

    • Life cycle mimics moss, but sporophyte is the major stage.

  • Phylum Monilophyta includes:

    • Equisetopsida (Horsetails):

      • Characterized by needle-like leaves, photosynthesis mainly in the stem, silica for rigidity, and bisexual gametophytes.

    • Psilotopsida (Whisk Ferns):

      • Lack roots and leaves (a reversal in evolution); photosynthesis occurs in stems.

    • Polypodiopsida (True Ferns, 20,000 species):

      • Large fronds that are photosynthetic and carry reproductive organs (sori = sporangia).

      • Sporophyte is the dominant life stage.

Importance of Seedless Plants

  • Mosses and Liverworts:

    • Fundamental in primary succession,

    • Replenish soil nitrogen via symbiotic fungi,

    • Serve as biological indicators of ecosystem health.

  • Ferns:

    • Aid in weathering of rocks and slowing of soil erosion.

    • Peat moss is significant as a bog plant used as fuel.

    • Cultivation of commercial plants like blueberries and cranberries, and used in floral arrangements.

    • Historical food source for terrestrial animals.