It's happened again, this time with the Mt. Diablo buckwheat (Eriogonum truncatum).
The Mount Diablo buckwheat, Eriogonum truncatum, "has been a Holy Grail in the East Bay for several decades," according to UC Berkeley botanist Barbara Ertter, who confirmed the identification in the field on Friday. Last reported in 1936, the flower was presumed extinct, she said, because its habitat has been overrun by introduced grasses. It is one of only three plants, all of them rare, that are endemic to Mount Diablo.
There are some nice photos of the plant in flower in the article.