Unit 3: Bryophytes

Syllabus Reference: Classification, reproduction, structure of sporophytes, evolutionary trends in Riccia, Marchantia, Pellia, Porella, Anthoceros, Sphagnum and Polytrichum. Economic importance [cite: 479-480].

1. Distinguishing Features & Classification

• Habit: Small, damp-loving plants.
• Body: Thalloid (flat, sheet-like) or Foliose (leafy).
• Vascular System: Absent (Atracheophytes). No xylem/phloem.
• Roots: Absent. Anchored by rhizoids.
• Lifecycle: Haplodiplontic. Gametophyte (n) is dominant; Sporophyte (2n) is dependent.

Classification (Rothmaler/Proskauer)

1. Hepaticopsida (Liverworts): e.g., Riccia, Marchantia, Pellia, Porella. Flat thallus.
2. Anthocerotopsida (Hornworts): e.g., Anthoceros. Horn-like sporophyte.
3. Bryopsida (Mosses): e.g., Sphagnum, Polytrichum. Leafy gametophore.

2. Evolutionary Trends in Sporophytes

A major evolutionary trend in Bryophytes is the Progressive Sterilization of Sporogenous Tissue. The sporophyte becomes more complex and sterile (non-spore producing) tissues increase to support spore dispersal and nutrition.

A. Riccia (Simplest Sporophyte)

• Structure: Only a capsule. No foot or seta.
• Composition: Mass of spore mother cells enclosed by a single layer of jacket cells.
• Sterilization: Minimal. Almost all inner cells become spores.

B. Marchantia

• Structure: Differentiated into Foot, Seta, and Capsule.
• Sterilization: Increased. Presence of sterile Elaters (hygroscopic structures) mixed with spores to help in dispersal.

C. Pellia & Porella

• Intermediate complexity between Marchantia and Mosses.
• Pellia: Capsule has a massive foot and long seta. Elaters are fixed (elaterophore).

D. Anthoceros (Hornworts)

• Structure: Foot and a long, horn-like Capsule (No seta).
• Evolutionary Leap: The capsule wall has stomata and chlorophyll, making it semi-independent (can photosynthesize).
• Sterilization: Presence of a central sterile column called the Columella.

E. Sphagnum & Polytrichum (Mosses - Most Complex)

• Sphagnum: Capsule is elevated by a pseudopodium (gametophytic tissue).
• Polytrichum: Highly differentiated sporophyte (Foot, Seta, Capsule).
• Capsule Complexity:
  • Apophysis: Photosynthetic region with stomata.
  • Theca: Spore-producing region with trabeculae.
  • Operculum & Peristome Teeth: Complex mechanism for spore dispersal.
• Sterilization: Maximum. Only a small fraction of cells become spores.

3. Economic Importance of Bryophytes

Focus mainly on Sphagnum (Peat Moss):

• Peat Formation: Sphagnum grows in acidic bogs. When it dies, it doesn't decay fully due to acidity, forming compressed carbonized matter called Peat. Used as fuel in some countries.
• Absorbent Packing Material: Dry Sphagnum can hold 20x its weight in water. Used by florists to pack live plants/flowers for transport.
• Surgical Dressing: In World War I, it was used as antiseptic dressing for wounds due to its absorptive and acidic (antibacterial) nature.
• Soil Conditioner: Added to soil to improve water holding capacity.