1978 – The Smithsonian included the San Diego ambrosia in a report identifying threatened, endangered and extinct plants in the United States, which the U.S. Fish and Wildlife Service chose to ignore for nearly twenty years.
January 9, 1997 – The Center and the California Native Plant Society jointly submitted a citizen petition to the U.S. Fish and Wildlife Service to list the San Diego ambrosia under the Endangered Species Act.
October 1, 1998 – After the Service refused to process the listing petition, the Center and the California Native Plant Society filed a lawsuit to list the San Diego ambrosia as an endangered species.
April 19, 1999 – In response to a Center lawsuit, the Service issued a positive 90-day finding on the listing petition but then stalled the process by refusing to take the next step.
December 29, 1999 – As a result of another Center lawsuit, the Service was forced to issue a proposed listing rule.
July 2, 2002 – Owing to the Center's persistent work, the San Diego ambrosia finally won protection under the Endangered Species Act and was listed as endangered.
December 19, 2007 – The Center filed suit to force the Service to designate critical habitat for the San Diego ambrosia, as well as challenging illegal critical habitat decisions made for 12 other species.
April 11, 2008 – The Service agreed to publish a critical habitat proposal for the San Diego ambrosia by August 20, 2009, with a final designation to be made one year later.
August 27, 2009 – The Service proposed to designate 802 acres of protected habitat for the San Diego ambrosia.
November 30, 2010 – The Service designated 783 acres of critical habitat for the San Diego ambrosia.
May 5, 2016 – The Center and allies filed a lawsuit challenging Riverside County's approval of a plan to trade away more than 40 acres of important habitat for endangered plants, including San Diego ambrosia, to a private developer.