A desert plant’s weathered beauty tells the story of strength and endurance in Jillian David’s “Agave.” A succulent plant native to the tropics and subtropics, the agave is not a cactus, but part of the lily family. Growing slowly, it dies after blooming only once. The stalk of its impressive flower weighs several pounds, and the whole plant serves numerous purposes. Its flower is edible, the stalk can be eaten, its syrup can be used instead of sugar and, perhaps most importantly, it is used to make tequila.