Environmentalist Judy Johnson speaks during public comment at a February meeting of the City Council, a precursor to her controversial appearance Monday.

A tree lover gave an explosive start to Monday’s meeting of the City Council, filibustering loudly with a personal attack against councillor Denise Simmons while the mayor gaveled repeatedly for order and councillor Ken Reeves spoke over her in anger and upset.

“Where was councillor Simmons?” said Judy Johnson, founder of the Cambridge Tree Stewards, recalling the issue of four large shade trees on Gilmore Street taken down a year ago — to benefit a single property owner, according to Johnson. Looking at a policy order Simmons filed Monday about an “unhealthy tree” threatening the seniors at the Truman Apartments on Eighth Street, she called Simmons a hypocrite interested only in getting re-elected in November.

As her diatribe went on, Mayor David Maher asked her to direct her comments to him, not Simmons, and had to resort to banging his gavel to get her attention as she ignored him and kept talking, reading from prepared remarks.

“We have not had this in 22 years. We’ve been able to control our meetings,” Reeves said loudly, adding a third voice into the mix. “This is an embarrassment.”

The cacophony went on for nearly four minutes. Johnson left immediately after ending her remarks.

Reeves’ comments had a double edge — a rebuke of Johnson and her attack on Simmons and of Maher, who took the mayor’s seat after a prolonged and divisive council voting process after the 2009 elections. Reeves, as the longest-serving member of the council, had been interim mayor while the councillors took repeated votes to end a three-month deadlock; he had spoken especially of wanting to serve as mayor on the School Committee, which he felt needed another person of color to reflect the diversity of the city and student body.

Reeves served as mayor three times before, in consecutive terms 1992-95 and in 2006-07.

This is also not the first Johnson has used the council’s public comment period in a controversial way. In February she was cut off when she went off-topic and began talking about City Manager Robert W. Healy’s pay. Notoriously, Maher broke his gavel that night, the Cambridge Chronicle reported alongside a video in which councillor Tim Toomey says Johnson has “gone beyond the bounds of decency.”