Daf Yomi - Sukkah 32 - Himnik

Rav Papa states that the Mishna which rules that a lulav which is cracked is disqualified is referring to a case where it split and the two leaves are going in opposite directions. This is called a 'himnek' and Rashi explains that it is similar to a scribe's quill. The Rambam rules that it is invalid if the two parts of the leaf are dstanced from each other to such a degree that they appear like two separate leaves. The Reoh states that the leaf is opened a lot.

Sheorim Mitzuyanim B'halacha states that the bochurim from Yeshiva who ask him about lulavim, showing him that there is a split on the top and they inquire if the lulav is disqualified because of being a himnik. He rules since it can only be seen after gazing at the top of the lulav for a long time and the leaves are only separated a fraction from each other, this is not what the Gemora had in mind and therefore it is a valid lulav.

There is no picture in that sefer, however the poskim do not rule like him and the defining factor seems to be if the leaves are heading in two opposite directions. Make sure you bring your lulav to a Rav for an individual ruling.