The Four Species/Arba’ah Minim
The other significant mitzvah of Sukkot is the taking up of the Arba’ah minim – the four species. Commonly, we know these as the lulav and the etrog- the palm branch and the citron. The other two species that are attached to the lulav are the myrtle branches called hadasim and the willows called aravot. The Bible source, again in the Book of Leviticus reads, “On the first day, you shall take the product of the Hadar tree, branches of palm trees, bough of leafy trees and willows of the brook and you shall rejoice before the Lord for seven days”.
The waving of the lulav and etrog, when reciting verses from Psalm 118, is done holding the lulav with the spine in the left hand and the etrog in the right (although there is a custom that lefties may switch sides). Held together, they are waved in 6 directions: to the front, to the right, to the back, to the left, upward and downward.
The lulav and etrog are not used on Shabbat for the same reason that the shofar is not sounded on Rosh Hashana if it falls on Shabbat. That is, to prevent the desecration of Shabbat.