Rabbi Yehuda says: Any plant that has white sap when it is cut may be used as bitter herbs. Rabbi Yoḥanan ben Beroka says: Anything whose surface is light green may be used as bitter herbs. Others say: Any bitter herb that has sap and whose surface is light green is fit for this mitzva. Rabbi Yoḥanan said: From the statements of all these Sages, we can learn that a bitter green herb has sap and its surface is light green. Rav Huna said: The halakha is in accordance with the opinion of Aḥerim. Ravina found Rav Aḥa, son of Rava, searching for merirata to use as bitter herbs. He said to him: What is your opinion, that you seek this particular herb? If you are looking for that which is most bitter, but we learned ḥazeret first in the mishna, which indicates that this is the preferred choice.
Rabbi Oshaya said: The optimal fulfillment of the mitzva is with ḥazeret, and Rava said: What is ḥazeret? It is lettuce [ḥassa]. The Gemara explains: What is the meaning of lettuce [ḥassa]? It refers to the fact that God has mercy [ḥas] on us. And Rabbi Samuel bar Naḥmani said that Rabbi Yoḥanan said: Why are the Egyptians likened to bitter herbs in the verse: “And they embittered their lives” (Exodus 1:14)? This comparison serves to tell you that just as these bitter herbs are soft at first and harsh in the end, so too, the Egyptians were soft at first, when they paid the Jews for their work, but were harsh in the end, as they enslaved them. This idea applies solely to ḥazeret, which has a bitter aftertaste, but not to other types of bitter herbs, which are bitter from the beginning. Rav Aḥa, son of Rava, said to Ravina: I retract my position and concede that it is preferable to use ḥazeret for bitter herbs.
Rav Reḥumi said to Abaye: From where is it known that this bitter herb that must be eaten on Passover night is a type of vegetable? Perhaps one could say that the mitzva should be performed with the bile of a kufya fish,which is very bitter, but not necessarily with a type of plant? He answered: Bitter herbs are similar to matza; just as matza must be prepared only from food that grows from the ground, so too, bitter herbs must be from food that grows from the ground. The Gemara answers: Bitter herbs are similar to matza; just as matza is prepared from a type of plant, but not including a tree, so too, bitter herbs must be from a type of plant that is not a tree.
Rabba bar Rav Ḥanin said to Abaye: I can say that the bitter herb mentioned in the Torah includes merely one species, i.e., only the bitterest plant can be used for this obligation. Abaye responded: For this reason it is written: “Bitter herbs” (Exodus 12:8) in the plural, indicating that many types of bitter herbs are fit for this purpose. Rabba retorted: But one can say that “bitter herbs” refers to two different species, but no more. Abaye explained: Bitter herbs are similar to matza; just as matza can be prepared from many types of grain, so too, bitter herbs can be taken from many different types of vegetables.