A fruit was said to acquire its name when Christian missionaries first saw the plant in South America. In its flower they saw the crown of thorns and other symbols of the crucifixion. What is it?

The fruit you're referring to is the passion fruit. Christian missionaries associated its flower with symbols of the crucifixion, such as the crown of thorns and the nails, which led to the name "passion" fruit, referencing the Passion of Christ. This connection highlights the fruit's significance in both botanical and cultural contexts.