If two substances share the same origin, are they considered the same genus even if their intended uses differ?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
If two substances share one common origin, they constitute a single genus, even if their intended purposes diverge. Examples include various oils derived from a single source like rose, violet, mercury, or jasmine, which all remain one genus if originating from a singular base oil. This is the sound position within the Shafi'i madhhab. The justification is that these substances are fundamentally the same base material (e.g., sesame oil), merely scented with aromatics, and thus retain their original classification, similar to how scenting other types of genera does not change their classification.
Supporting text
A secondary opinion suggests that in cases where scenting agents are used (like floral oils), the resulting product does not fall under the rulings of Ribawi items because the intended purpose is not consumption. Furthermore, Abu Hanifa holds that they are distinct genera because their intended uses are different.