Step 1: Understanding the Concept:
Methylxanthines are a group of alkaloids including caffeine, theophylline, and theobromine. They are well-known CNS stimulants.
Step 2: Detailed Explanation:
1. Camellia sinensis (Tea): This is the primary source of tea leaves. Tea contains caffeine (a methylxanthine) and small amounts of theophylline and theobromine.
2. Stimulant Action: Caffeine acts as a central nervous system stimulant. While its primary mechanism is adenosine receptor antagonism, the resulting alertness and physiological stimulation share similarities with the stimulant effects of nicotine.
3. Others: Theobroma coca (Coca) contains cocaine (an alkaloid, but not a methylxanthine). Ephedra contains ephedrine (sympathomimetic). Atropa contains atropine (anticholinergic).
Step 3: Final Answer:
Tea (Camellia sinensis) is the source of the methylxanthine-based stimulation commonly consumed by humans.