I have often been puzzled by the presence of two reserved spots on many seder plates for the same role during the evening's festivities. The "Maror" segment (just after making the berakhah over the matzah and just before eating the Korekh, the sage Hillel's sandwich), includes the unique berakhah,
Barukh attah Adonai, Eloheinu melekh ha'olam, asher qiddeshanu bemitzvotav, vetzivanu al akhilat maror.
Praised are You, Lord, our God, Ruler of the universe, who has sanctified our lives through His commandments, and commanded us to eat maror.
On some seder plates, you will find only a spot for maror. On others, you will find an additional one for "hazeret," which is also a type of maror. Confused? Me too.
The source for this mitzvah is Exodus 12:8, which states that the Israelites were commanded to eat the Paschal Lamb with something called merorim, the plural of maror, and it is unclear what was meant here. According to the JPS Torah Commentary, maror "probably referred originally to the kind of pungent condiment with which pastoral nomads habitually season their meals of roasted flesh."
But the rabbis of the Mishnah, trying to interpret for their day (that is, the first couple of centuries of the Common Era), stated that this mitzvah can be fulfilled by eating one of five different types of vegetables. Problem is, we do not know what most of them are!
Today, the practice among most of the Diaspora is to use horseradish, which for my entire life has been the traditional understanding of the word maror. Israeli Jews, however, generally use Romaine lettuce, which is known as hazeret. Hence the presence of the additional spot on the seder plate.
Rabbi David Golinkin just produced a new teshuvah on the subject, and it makes for a great historical romp through the pungent condiments of the Middle East and Eastern Europe. Check it out here.
I won't spoil the surprise, but remember that whatever the answer, your family's custom is still your family's custom, and I wouldn't go changing anything at home merely on the basis of one rabbi's deduction. Pesah is a joyous festival of freedom, not an opportunity to tell your grandparents that they have been misled for their whole lives. Enjoy!
Rabbi Seth Adelson