Is there any significance, halachic or otherwise, to the holder (or koishele) for the hadassim and aravot on the lulav? Who is the earliest source to describe it? Who (other than Chabad) doesn't use it.
Inspired by this thread on KAYJ.net
The Sefer Nitei Gavriel perek 40:3: with footnote 5 brings many sources starting with the Shu"t Agurah B'oheilecha pg 12(could not find it but see Pischei Tshuva who quotes it).
The Mishna Brurah seif katan 8 quotes it as well:
ח) בקשר גמור - ולא בעניבה דאין זה קשר הנאסר בשבת ויו"ט ולא מקרי אגד ועיין בתשובת אגורה באהלך שמצדד דמה שנוהגין העולם שלא לעשות קשר אלא עושין מן עלי לולב כמין בית יד ותוחבין הלולב בו ג"ז בכלל קשר ע"ש:
The Pri Megadim Eishel Avrham siman 647 writes that he is noheg like this. The Aruch Hashulchan 651:7 writes that its nice for the mitzva and he is also noheg like this.
The Tamei Minhagim Os 792 brings from the Belezer Rebbe a reason of praise for such a minhag to use it, he brings the Beis Yosef 651 as the source for bringing the 4 minim together and the Beis Yosef quotes the Rekainti that the daled minim represent the 4 letter name of HaShem ,the Belzer Rebbe notes that since the 4 letter name needs to have a slight separation between each other so does the daled minim which represent it.
For those who oppose to it the Nitei Gavriel perek 40:2 footnote 4 brings the Shulchan Aruch (Sefardim) the Leket Yosher pg 147 to only tie the lulav,the Chasam Sofer in his Chiddushim to sukka daf 36b DH b'mino who holds only a knot ontop of a knot,also see the Bikurei Yaakov 8 ,and the Kaf Hachaim 11 who oppose it.
The Arbaat Haminim must be held together while "netilt lulav". Some use koishele and some just simple thread (usually made of lulav itself). So halakhic significance is holding it together. However some claim (there opinion is not accepted by majority) that it is hozez (some even remove finger rings because of it before the netila).
As pointed out seems like it is Ashkenaz invention - very convininent - I am using it myslef. :)