First Fossil Fruits and Leaves of Burretiodendron s.l. (Malvaceae s.l.) in Southeast Asia: Implications for Taxonomy, Biogeography, and Paleoclimate

Premise of research. Burretiodendron Rehder is a genus of six species that are mainly found on limestone in Southeast Asian mountain forests with a monsoonal climate. Recent molecular evidence supports its placement in Malvaceae s.l. Presently, two species of Burretiodendron have been classified as vulnerable according to the International Union for the Conservation of Nature. Fossil Burretiodendron is also extremely rare in the record, and little is known about its evolutionary history. Methodology. Fossil fruits and leaves were collected from upper Miocene sediments in Yunnan (SW China). Their macro and micro morphology were studied and compared with all extant species of Burretiodendron and with species of fossil and extant Craigia W.W. Sm. & W.E. Evans having somewhat similar fruits. Pivotal results. We recognize fossil remains of Burretiodendron on the basis of fruits described as Burretiodendron parvifructum sp. nov. and associated leaves of Burretiodendron miocenicum sp. nov. Conclusions. These Miocene fossils are the first confirmed occurrence of this genus in the Southeast Asian fossil record. This discovery supports the possibility that southeastern Yunnan was already experiencing frost-free winters and seasonal precipitation with wet summers and relatively dry winters. It also corroborates the hypothesis that this genus might have originated at the Sino-Vietnamese border, where the biodiversity center of the genus is today.