How is the principle of 'like for like' applied when exchanging items of the same genus but different species or varieties?

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When two things share a specific common name, they constitute a genus (jins), such as the different varieties of dates or types of wheat. All dates are one genus because the specific name 'dates' encompasses them, even if the varieties differ, such as Barnī, Ma'qulī, Ibrāhīmī, and Khāstawī. For any two items that share the same genus, the legal ruling prohibiting unequal exchange applies, even if the species (anwā') differ, based on the Prophet's saying: "Dates for dates, like for like, and wheat for wheat, like for like." Equality was required based on the genus (dates for dates, wheat for wheat).