Yosef Karo

“ That is why in these countries, we ab initio use these myrtles that are imported and do not have three leaves from one node. There is one who says that our myrtles are not considered wild myrtle because they are two by two and are not like the wild myrtle in the Gemara. ”

“ In order to hinder fulfilling the obligation, a majority suffices (even if it is not at the top) (Tur) .
סעיף ה
למצוה בעינן כל שיעור אורך ההדס שיהא עבות ולעיכובא ברובו [ואפי' אינו בראשו] [טור] :
646:6 If they completely dry out, they are invalid. If they are slightly dried, they are valid. ”