Yosef Karo, Translation:Shulchan Aruch — Orach Chaim 650…
“ The measure of the myrtle and willow ends up being 2.5 [normal] tefachim, which is ten godels. The measure of the spine of the lulav is thirteen and a third godels. There is one who says that the minimum size of the lulav spine is fourteen godels. And there are those who say that the minimum size of the myrtle and willow is twelve godels and the minimum size of the lulav spine is sixteen godels (and we do this, preferrably) . ”
