Joshua Kosman May 4, 2021 Christine Goerke (left) as Elektra and Michaela Martens as her mother, Klytemnästra, in Richard Strauss’ “Elektra” at San Francisco Opera. Photo: Cory Weaver Mother’s Day, by tradition, is a day for the sentimental celebration of those central women in many of our lives. She may not necessarily be the kindly, nurturing figure of the greeting cards (those of us who got lucky in this department should always spare a moment of sympathetic support for those who didn’t), but Mom is generally a focus for our love and gratitude. And since opera is a reflection of the most primal emotions of the human situation — love, death, family and so forth — you might expect to find mothers playing a similarly central role in the stories that composers have been telling for centuries through music.