MARAN is posek like RAMBAM, that most defects in the arba minim are kosher after the first day. A question that I have always had is, does this mean that if most of the leaves have fallen off the aravah or hadas it would still be kosher, at least for Sepharadim? Or would that be considered “Chaser Sheur”, that is pasul all the days? If an aravah that has lost most of its leaves is kosher, how about a hadas? Would it be the same, or would it be a problem that it is not considered עבות, and therefore not the right species?
If most of the leaves have fallen off, whether hadassim or aravot, they are not kosher on all days.
When we say “most”, this only applies to the minimum shiur. For example the shiur of aravot is 3 tefachim. If your aravot are 4 tefachim and half the leaves fell off, you still have the majority of the required shiur and it’s kosher.