Kerr's Sycamore

Platanus kerrii (Kerr's plane) is a rare and distinctive species of plane tree (sycamore) native to the subtropical and tropical forests of Vietnam and Laos in Southeast Asia. It is the only extant member of the subgenus Castaneophyllum, and is the sister group to all other lineages within Platanus. Unlike all other plane trees, P. kerrii is evergreen and retains unlobed leaves throughout its adult life, with none developing the lobed form characteristic of other Platanus species. While some have speculated that P. kerrii might represent a living analogue of ancestral plane trees, no fossil material clearly displaying its distinctive morphology (such as its pollen morphology) has been found. Even its distinctive leaf form, once thought to reflect a primitive condition linking it to Cretaceous ancestors, is now understood as a derived feature rather than evidence of direct ancestry from early Platanus-like forms.