Excerpts from Jim Conrad's
Naturalist Newsletter

sunburned leaves of seedling Royal Palms

from the September 12, 2010 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO

Last week we saw that many Maya believe that rain falling during our current rainy-season afternoon storms burns the plants it falls on. I'm skeptical about that, but I know for a fact that leaves can suffer serious burn from the sun.

We have many potted Royal Palm seedlings growing in deep shade. They need to be moved into sunlight bit by bit, so the other day I moved some to a sunnier spot but misjudged how much sunlight they'd get. The resulting white "killed areas" -- where the blades' bent surfaces faced directly against the sun -- appear above.

The same happened with a Ramon tree. Its sunburned leaf with blotches of dead and dying tissue is seen below:

sunburned leaves of Ramon, Brosimum alicastrum

The Ramon leaf is interesting because when I moved the seedling the leaf was just unfolding leaf a top the seedling's stem. Leaves below it didn't suffer, apparently because they'd been hardened enough over time. Leaves developing later above the damaged leaf didn't suffer either, because as they unfolded they could adjust their defenses to the increased sunlight. Clearly, Ramon saplings can accommodate a range of sunlight intensities, but at least their young leaves are vulnerable to sudden changes.