Step 1: Understanding the Concept:
Colchicum (Autumn Crocus) is a plant-based drug used primarily for inflammatory conditions, especially gout.
Step 2: Detailed Explanation:
1. Colchicine: This is an amino-alkaloid found in the seeds and corms of \textit{Colchicum autumnale}.
2. Mechanism: It works by inhibiting microtubule polymerization in white blood cells (neutrophils). This prevents the migration of these cells to the site of inflammation, thereby reducing the pain and swelling associated with acute gouty arthritis (a type of rheumatism).
3. Others: Vinblastine is an anti-cancer agent from Vinca. Reserpine is for hypertension. Podophyllotoxin is for warts/cancer.
Step 3: Final Answer:
Colchicine is the unique active constituent of Colchicum used for its potent anti-rheumatic (anti-gout) activity.