Pseudobark

Fossils still live among us, from crocodiles to chickens to trees.  Many palms and related plants retain very primitive traits that worked for them.  In this case, a yucca tree uses dead leaves and their stems to form an insulating "bark."  This one has been pruned, but unpruned palms and yuccas develop "beards" of dead leaves that not only insulate the plant's trunk, like bark on more modern trees, but also form entire, very local ecosystems.