The Mishna (23a) brings Rabbi Elai as quoting his teacher, Rabbi Elazar as teaching a number of laws about eiruvin, and, as an aside, a rule about the Passover holiday. The rules about eiruvin were:
that even an area the size of a Beit Kor – an area much larger than 500 square amot (a kor equals 30 se’ah, so a Beit Kor is equivalent to 75,000 square amot) – could be walled off and considered a private domain, and
that if one member of the courtyard neglected to participate in the eiruv, his house was not considered part of the eiruv and nothing could be carried in or out of his house, but the eiruv is valid for the rest of the courtyard.
The rule related to Pesah that was related by Rabbi Elai was that a wild plant called Arkablin can be used as Maror (bitter herbs).
Rabbi Elai laments, however, that although he remembered learning these rules from Rabbi Elazar, he could not find anyone else who recalled those teachings, leading him to fear that perhaps his memory was faulty and that his teacher had not taught those halakhot.
A number of different suggestions have been made about the identification of the Arkablin plant, or, according to a variant reading, the Akrabin (scorpion) plant. It is also possible that the Talmud, itself, refers to more than one plant when describing its attributes. One of the possible identifications is one of the Heliotropium plants, which have the shape of a scorpion’s tail. These plants are wild grasses that grow in a number of places in Israel. Occasionally they are domesticated for their beauty and fragrance, as well as for medicinal purposes.
Resh Lakish identifies the plant as Atzvata Haruziyata, which may be identified with a thorny, climbing plant, Euphorbia officinalis.
Although the Gemara in Massekhet Pesahim (39a) relates that Rabbi Elai eventually found that Rabbi Eliezer ben Yaakov remembered the rule about Arkablin, none of the three of the laws quoted by Rabbi Elai in the name of Rabbi Elazar, are accepted as normative halakha.