Portraits of pugilists, a key L.A. collagist gets his due, and a piano show about destruction

An influential pioneer of assemblage. Intimate portraits of fighting men. And a show that captures odd clay sculptures in paint. Plus: Flower paintings in time for Mother's Day and a pair of piano performances — one of which features an ax. Here are seven shows to see this week (and next):

Berman, “American Aleph,” at Kohn Gallery. This is the first comprehensive Los Angeles retrospective for the pioneering Southern California assemblage artist in roughly four decades. The artist, who was also the publisher of the influential arts and literary magazine Semina, had an international influence. The exhibition gathers works from the 1940s to his death in 1976, including numerous examples of his Verifax collages, photocopied and painted assemblages that play with the tropes of popular culture. This is one not to miss.