A Joshua tree in California.
Joshua tree definition by Webster's New World
Origin: uncertain or unknown; perhaps Mormon coinage on the fancied resemblance of the angular branches to the arms of Joshua leading the Israelites
Joshua tree definition by American Heritage Dictionary
Origin: Probably after Joshua1, from the resemblance of the tree's greatly extended branches to Joshua's outstretched arm as he pointed with his spear to the city of Ai (Joshua 8:18).