Fossil flowers of <i>Ayenia</i> (Malvaceae) preserved in amber: evidence for lianas in Miocene rainforest of Southeast China

Abstract Background and Aims Floristic diversity and paleoclimatic estimates revealed that the Middle Miocene Zhangpu flora from Southeast China was a diverse ancient tropical rainforest, but our knowledge on the structure and ecology of this rainforest is still limited. Here we report the presence of lianas in the Zhangpu flora based on exquisitely preserved fossil flowers of Ayenia. Methods Two fossil flowers, preserved in amber, were investigated with light microscopy and X-ray tomography, and are described herein as Ayenia zhangpuensis sp. nov. and Ayenia sp. Key Results The flower of Ayenia zhangpuensis is bisexual and pentamerous. Its sepals are ovate, the petals are clawed, with an inner ridge on their hood delimiting a fossa, together forming a lantern-like corolla around the androecium and gynoecium. The androecium forms a campanulate staminal tube; the gynoecium is syncarpous with a superior ovary. The other specimen, treated informally as Ayenia sp. differs from A. zhangpuensis in having more incurved and elongate sepals. The two fossil flowers closely resemble extant flowers of the Ayenia section Vahihara (former Byttneria section Vahihara), almost all species of which are unarmed lianas thriving in humid tropical conditions. Conclusions The striking similarities between fossil and extant flowers of the Ayenia section Vahihara suggest a morphological stasis in floral structure within a tropical liana lineage since at least the mid-Miocene. Together with other climbing plants known from the Zhangpu flora, our study shows that this Miocene rainforest is comparable to modern Southeast Asian rainforests in both floristic composition and inferred forest structure.