To the uninitiated, the boysenberry may look like a big, blowzy, underripe blackberry, but it is in fact a noble fruit, as distinct from a common blackberry as a thoroughbred is from a mule. Large, dark purple, juicy and intense, it derives its unique flavor from its complex ancestry: sweetness and floral aroma from its raspberry grandmother, and a winy, feral tang from three native blackberry species. It's a California classic, emblematic of the joys of growing up in the Southland before it succumbed completely to sprawl. And it's all the more precious, despite its near extinction in this state,...