There are many cases, in which two pure species, as in the genus Verbascum, can be united with unusual facility, and produce numerous hybrid offspring, yet these hybrids are remarkably sterile.
Kasu asko dira, Verbascum generoan adibidez, bi espezie garbi ezohiko erraztasunez bat daitezkeenak eta ondorengo hibrido asko sor, eta, hala ere, hibrido hauek nabarmenki antzuak dira.