Complex sentence: The lemony smell is strong enough to be noticed by humans standing nearby, and by rubbing across the plant, without picking leaves, and is reputed to repel mosquitos for as long as 20 minutes.
Split into simpler sentences: The lemony smell is strong enough to be noticed by humans simply standing nearby. Simply rubbing one's arms across the plant, without even picking leaves, is reputed to repel mosquitos for as long as 20 minutes.