Tuesday, February 21, 2012

Winter buds: Pecan and hickories

The terminal of a pecan twig
      Ever take a close look at pecan buds in winter. You can learn a lot about trees just by observing how buds are arranged on the twig. In the photo at left, you can see the terminal bud and several lateral buds of a pecan stem. Note that the terminal bud looks much different than all the lateral buds. The terminal bud looks like a collection of tightly compressed leaves formed into the shape of praying hands. It is from this bud that the pistillate flowers will emerge this coming spring. The lateral buds are tear-drop shaped and are completely covered by a protective scale.  Within each of these lateral buds is a vegetative bud flanked by catkins on each side. You can see how these lateral buds develop in the spring here.

Primary, secondary, and tertiary lateral buds
     There is one more interesting bud feature on pecan trees.  You will find at least 3 buds at each node. In the photo at right, you can see 3 buds lined up above the leaf scar. The large bud on the top is the primary bud. Underneath are secondary and tertiary buds that are formed to provide reserve growing points in case the primary bud is lost to mechanical injury or frost.  We discovered the importance of secondary buds when almost all primary buds were killed during the Easter freeze of 2007.

Terminal buds of four members of the hickory family
    Now that we've looked at pecan buds, I thought it would be interesting to see how pecan compares to other members of the hickory family (photo at right).  Within the hickory family there are 2 major groups: the pecan hickories and the true hickories. The pecan hickories are represented in the photo by pecan (of course) and bitternut hickory. These hickories have "valvate" terminal buds (the praying hands). Bitternut hickory is easily identified in the field by its bright, rusty-orange buds.  The true hickories have scaly buds are are represented in the photo by the shellbark and shagbark hickories. Also note the immense size of the terminal buds of the true hickories.
Buds of a pecan, shellbark hickory, and its hybrid (hican)
     While we are looking at photos of buds, lets look at a naturally occurring hybrid hickory commonly called a "hican".  In the photo at right, you can see the buds of a pecan, a shellbark hickory, the the cross of these two species (the hican). Note that the terminal bud of the hican is not as scaly as the true hickory but it doesn't look anything like a pecan terminal bud. It seems when these two species cross, the progeny seem to favor the true hickory side of the family.