Last week, while photographing dormant buds, I noticed some eerie, finger-like protrusions on the terminal branch ends of a shellbark hickory, seen in the image above. These spent parts are actually the petioles of last season’s foliage. For some reason, these petioles remain on stems through autumn and into winter, long after leaves have changed color and fallen.
Marcescence is the retention of dead plant parts that are typically shed during the season. It is commonly observed in Fagaceae, especially among oaks and beeches, which sometimes hold on to spent leaves throughout winter. These leaves are finally abscised in spring, as new foliage begins to appear. In the image below, you can see the base of a petiole splitting from the stem. A leaf scar will remain, showing the vascular connections between the leaf and stem.
So why does the shellbark hickory retain its petioles? Some have hypothesized that trees hold on to spent leaves in order to protect tender buds and twigs from hungry herbivores during the winter. It’s possibly that the hickory bears its left-over anatomy as a protective measure against animals that might seek out the precious buds hidden among this spiky armor. Either way, these curved petioles have an ominous presence in the stark winter landscape.