What makes a tree a tree? Or rather, why can we recognize trees in even quite abstract depictions when they are so varied in nature? Researchers have found a clue in the branches, and used math to ...

The artist Scott Kildall is waving his hand over the contours of a Joshua tree, just inches from its spiky green, bayonet-like leaves. "If I get too close to it, it will prick me and draw blood," he ...