After reading a passage about Tu B'Shevat "marking the end of the season of major rain," the rain splattering against the roof became a sudden downpour. The group broke out in laughter.

"Special effects!" someone joked, as guitarist Renee Rubin drummed a few notes, signaling it was time for a new round of songs

One of the lesser-known Jewish holidays, Tu B'Shevat is also known as the New Year of the trees. The custom of honoring the holiday by holding a special seder, largely modeled after that of Passover, was initiated by Jewish mystics, or kabbalists, in the 16th century.

Sitting around the festively decorated seder table at Menorah Park, some 40 participants — many of them singles in their 20s and 30s — sang and read passages from a special Haggadah created by Bay Area artist Claire Sherman. Throughout the service, led by Otzma alumnus Mark Beck, four cups of wine were served, along with a variety of foods mentioned in the Bible: olives, dates, figs, apples and walnuts.

The event was jointly sponsored by the Young Adults Division of the S.F.-based Jewish Community Federation, the Jewish National Fund and the Otzma Alumni Association.

JNF volunteer Carol Emold told the group that Jews have typically celebrated Tu B'Shevat by planting trees in their communities or providing money for the planting of trees in Israel.

Some singles expressed relief at the opportunity to get away from the "singles scene" and unite with couples in a more spiritual setting.

"I was intrigued by the idea of exploring the ecological origins of Judaism as part of a larger Jewish community. The fact that there are a lot of other singles here is a bonus, but not my main reason for coming," said participant David Fisch.

Because of its focus on the environment, the seder offered an event most young adults, regardless of their Jewish knowledge, could easily relate to, he said.

Beck, who stressed the importance of respecting the environment, said that trees should not be prized merely for their ability to be cut down or consumed. Rather, he said, it is worthy to honor them "simply for their beauty."

First-time seder participant Leslie Karren noted that even the "no shows" unknowingly contributed to the event. "Because of the rain, a lot of seats were left vacant. All the leftover food will now be donated to the homeless."

The event marked the first time YAD, JNF and Otzma joined forces to co-sponsor a Tu B'Shevat seder, which was coordinated by Jethro Busch of YAD, Emold of JNF and Beck of Otzma.

YAD, which is strictly for singles, provides educational, social and cultural programs for Jews between the ages of 21 and 39. The JNF serves as the official reforestation and agricultural development agency for Israel, while Otzma, housed at the S.F.-based Bureau of Jewish Education and funded through the JCF, provides fellowships for college-age Jews to live, study or volunteer in Israel.

The seder drew to a close as singles joined couples in raising the fourth cup of wine — a symbolic gesture connoting "the ruling of spring with its mature fruits whose blossoms were born on Tu B'Shevat."