The Leaf Fossil Of Tectona(verbenaceae) From The Pliocene Of Western Yunnan, China And Its Research Of Insect Herbivory

Tectona is a genus of tropical hardwood trees in the Verbenaceae. The three species Tectona grandis, Tectona hamiltoniana and Tectona philippinensis are native to southern and southeastern Asia. No Tectona fossil leaf record has been reported thus far. Here, we describe a fossil leaf of Tectona yunnanensis sp. nov., collected from the Pliocene Mangbang Formation in Tengchong, Yunnan Province, China as a new species, and its research of insect herbivory.The fossil’s morphological characteristics and anatomical characteristics were investigated by macro-observation and cuticular analysis, and were compared with its three extant species. The fossil is obovateshaped with entire margin. Its primary vein is pinnate, and five secondary veins are clearly visible. The secondary veins show dichotomous branches, and their exterior tertiary veins are looped. The cuticles of the fossil are hypostomatic, and the trichome bases are of the single-ring actinocytic type. The adaxial epidermal cells show no decoration and are rectangular in shape, and the fossil stomata are elongated-elliptic and haplocheilic.Comparison of fossil and extant species’ s herbivory traces was taken under SEM and EDS. The results showed that the characteristics of herbivory trace were lack of mesophyll but all veins were residual. This feature is similar to the insect damage of Pyransta machaeralis Walker or Pyralidae. It also indirectly proved that the Tengchong has survived Pyransta machaeralis Walker and Pyralidae during the Pliocene. It provided important information for the study of the co evolution of plants and animals in the western of Yunnan.The discovery of T. yunnanensis sp. nov. extends the reliable fossil record of Tectona to the Pliocene, demonstrates the importance of the evolutionary history of this genus in southwest China, and supports the theory that Tectona originated from eastern and southeast Asia.