As you drive up the Mt. Lemmon highway you soon leave the Saguaros behind and come into a landscape with oaks and a number of different shrubs. One of the most beautiful shrubs is called: Manzanita – a Hispanic name meaning “little apple”. The botanical name, arctostaphylos, comes from two words meaning “bear grape”. In the Spring and early Summer it is covered with beautiful pink or white flowers, shaped like little bottles.
On a recent plant walk, we noticed bright red shapes on the leaf margins of a manzanita. We suspected that these shapes were galls. My friend, Larry looked it up in a book about galls, and told me that it has its own name: Tamalia coweni.
Galls are an abnormal growth that plants create in response to the activity of little critters, like tiny wasps or, in this case, an aphid. The aphid gets on a leaf margin, and somehow tricks the plant into growing in an unusual way. The portion of the leaf with the aphid, swells, and the edge of the leaf rolls over. At first this growth is green. After a while it turns bright red.
This is my photograph of a leaf with two galls, one red and the other green. When we sliced the green gall open, we saw aphids inside, barely visible in the picture below. The aphids lay eggs which develop into adults that emerge from the leaf when they are ready.
We have seen galls on other plants, especially oak trees. Galls come in many different forms, all serving as a place where eggs are protected and fed on their way to their full development.