The question of the day: When is a leaf not really a leaf? Well, it could be when it's a spine, but today we're considering when it's only part of a leaf. Many leaves, called compound leaves, are subdivided into smaller parts that may look like leaves but aren't. How can you tell? Well, look in the angle formed by the stem of the leaf joining the stem of the shoot. A small bud in the angle is a giveaway that it really is a leaf; no bud, then it's a fraud.
Leaves formed of a central axis with leaflets coming off on either side are said to be pinnate, meaning featherlike, and are called pinnae. Sometimes, as in Honey Mesquite, the central axis divides into two parts, each with pairs of leaflets—thus having two pinnae. On the other hand, Screwbean Mesquite leaves usually have four pinnae. Another pattern is where leaflets diverge from a single point—a palmate leaf, as in the Coyote Gourd.
Many plants are difficult to identify—paying attention to leaves pays
off.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.