What's a Kikayon?

In the brief biblical book of Jonah, the prophet runs from a mission from G-d, escapes to a ship, encounters a storm, convinces them to throw him overboard to quell the storm, and spends the next 3 days pouring out his heart to G-d from the belly of a great fish.  The fish spits him back up, and G-d orders him off again.  This time around, Jonah complies, saves a city from its own immoral fate, and sits in a booth outside the city to watch. 
 
He’s angry with G-d, upset that he had to go to the city in the first place…because he knows that G-d would’ve forgiven them anyway.  Seeing that Jonah needs a lesson in the quality of mercy, G-d provides a plant to grow by Jonah’s hut.  It appears suddenly before the dawn, grows tall and sturdy with broad leaves to block the sun.  Jonah feels comforted, protected.