PTERIDÓFITAS – O GRUPO DAS SAMAMBAIAS, CONSIDERADAS FÓSSEIS VIVOS.
Introduction to Pteridophytes
Overview of Pteridophytes
- Pteridophytes, commonly known as ferns, are vascular plants that evolved with significant innovations such as the development of conductive vessels for nutrient and water transport.
- Unlike bryophytes, pteridophytes do not produce seeds and have distinct physical characteristics that differentiate their roots, stems, and leaves.
Structure and Function
- They possess specialized tissues called xylem (for water and mineral transport) and phloem (for transporting photosynthesis products).
- The evolution of these structures has allowed pteridophytes to grow larger and thrive in various light conditions.
Physical Characteristics of Pteridophytes
Root System
- Roots form a root system that anchors the plant in soil while absorbing water and minerals essential for growth.
Stem Structure
- Stems contain lignin, a polymer providing mechanical strength necessary for supporting larger aerial parts of the plant.
Leaf Functionality
- Leaves serve as photosynthetic organs equipped with stomata for gas exchange, crucial for the plant's survival.
Classification of Pteridophytes
Major Groups
- Pteridophytes can be classified into several groups including Lycopodiopsida (lycophytes), Equisetopsida (horsetails), Psilotopsida (whisk ferns), and Polypodiopsida (true ferns).
Lycopodiopsida
- Characterized by small, scale-like leaves; includes lycopodium plants known for their strobili which produce spores.
Equisetopsida
- Known as horsetails; features rough stems with reduced scaly leaves. Commonly found in moist environments.
Psilotopsida
- Comprises primitive plants like Psilotum; lacks true roots or leaves but has rhizoids instead.
Polypodiopsida
- Includes ferns like Samambaias which thrive in tropical regions; notable for their height due to unique root structures from the stem base.
Reproductive Cycle of Pteridophytes
Life Cycle Phases
- The life cycle involves two main phases: sporophyte (dominant phase visible in nature) and gametophyte.
Sporophytic Phase
- Begins with spore germination leading to the formation of gametophyte. Spores are produced by sporangia located on leaf undersides.
Gametophytic Phase
- The gametophyte is a flat green structure anchored by rhizoids producing male (antherozoids) and female gametes (ovules).
Fertilization Process
- Fertilization occurs when male gametes swim to female ovules resulting in a diploid zygote that develops into a new sporophyte, continuing the cycle.
Ecological Importance of Pteridophytes
Role in Ecosystems
- Crucial for ecosystem stability by preventing soil erosion, providing habitats, and contributing to carbon cycling through photosynthesis.
Human Utilization