Late Oligocene Fissistigma (Annonaceae) leaves from Guangxi, low-latitude China and its paleoecological implications

Fissistigma nanningense sp. nov. (Annonaceae) is described based on well-preserved mummified leaves from the Oligocene Yongning Formation of Nanning, Guangxi, southern China. They are characterized by retuse apex, a swollen petiole, eucamptodromous to simple brochidodromous secondary veins, percurrent tertiary veins, an obvious sub-vascular bundle and abundant oil cells. The nearest living relative of F. nanningense is considered to be Fissistigma glaucescens based on both qualitative morphological comparisons and the principal component analysis. The climbing habit of this genus indicates that a multilayered structure must have existed in the Oligocene forest of Guangxi. Moreover, according to the variation of leaf morphology in F. glaucescens under different environment, analogically, the present fossil leaves possessing small size and retuse apex indicate that they might grow in a sparse forest, or/and under the nutrient-poor conditions.