1️⃣ Systematic Position (Classification)
Kingdom: Plantae
Division: Rhodophyta (Red algae)
Class: Rhodophyceae
Order: Gelidiales
Genus: Gelidium
2️⃣ Habitat
Marine red alga
Found attached to rocks in shallow coastal waters
Common in warm and temperate seas
Prefers wave-exposed rocky shores
3️⃣ Thallus Organisation (External Morphology)
Multicellular, erect red alga
Thallus is cartilaginous (firm and elastic)
Thallus differentiated into:
Prostrate system (creeping, attached)
Erect system (upright, branched)
Branching is dichotomous or irregular
Size: generally small to medium
📌 Labelled diagram of Gelidium thallus is important
4️⃣ Internal Structure
Thallus shows pseudo-parenchymatous organisation
Differentiated into:
(a) Cortex
Outer pigmented cells
Photosynthetic
(b) Medulla
Inner colorless cells
Provides strength
5️⃣ Cell Structure
Cell wall composed of:
Cellulose
Agar-yielding polysaccharides
Pigments:
Chlorophyll a
Phycoerythrin (dominant)
Phycocyanin
Reserve food:
Floridean starch
No motile cells at any stage
6️⃣ Nutrition
Autotrophic
Photosynthesis in marine habitat
Red pigments help absorb blue light at depth
7️⃣ Reproduction in Gelidium
🔹 A. Vegetative Reproduction
By fragmentation
Detached thallus parts grow into new plants
🔹 B. Asexual Reproduction
By tetraspores
Tetraspores are:
Haploid
Non-motile
Formed in tetrasporangia
Germinate into new gametophytic plants
🔹 C. Sexual Reproduction
Type: Oogamy
Plants are dioecious
(a) Male Plant
Produces spermatangia
Spermatangia produce non-motile spermatia
(b) Female Plant
Produces carpogonium
Carpogonium has a long trichogyne
➡️ Fertilization occurs when spermatium fuses with carpogonium
8️⃣ Post-Fertilization Changes
Formation of carposporophyte
Carposporophyte remains attached to female plant
Produces diploid carpospores
9️⃣ Life Cycle
Triphasic life cycle
Gametophyte (n)
Carposporophyte (2n) – parasitic on female gametophyte
Tetrasporophyte (2n) – independent phase
Meiosis occurs in tetrasporangia
Produces haploid tetraspores
📌 Triphasic life cycle is a key exam point
🔟 Economic Importance of Gelidium
✔ Useful
Major source of agar
Used in:
Microbiological culture media
Food industry
Pharmaceuticals
❌ Harmful
No significant harmful effects
