Quercus L. is the largest genus in the family Fagaceae, with more than four hundred species. Cyclobalanopsis is considered as a subgenus of Quercus. Accurate identification of fossils facilitates better understanding of the geological history and the evolution of subgenus Cyclobalanopsis.
Prof. ZHOU Zhekun of Xishuangbanna Tropical Botanical Garden (XTBG) and his team collected some fossils from Xianfeng basin, 60 km north of Kunming, Yunnan Province (25°25′ N, 102°51′ E, 2200 m alt). They conducted a study with two goals: (1) to precisely identify a new fossil Quercus species based on leaf morphological and cuticular features; (2) to explore the evolutionary and ecological significance of the new fossil species.
To better determine the fossil species, the researchers compared their fossils with both extant and fossil species of subgen. Cyclobalanopsis. The results indicated that the fossils had the closest affinity with extant Quercus delavayi by possessing similar blade shapes, sizes, tooth types, venations and trichome bases, but cannot be assigned to any extant or fossil species. Therefore, they described them as a mew species, Quercus praedelavayi Y.W. Xing et Z.K. Zhou.
The researchers hypothesized that the Quercus species in dry environment had a higher trichome density than in humid region. To test the hypothesis, they counted the density of trichome bases of the Quercus praedelavayi and Quercus delavayi. The trichome base density of Q. praedelavayi was higher than the extant values. The results indicated that the evolution of trichome density of Q. delavayi was not driven by the decrease in precipitation. The study entitled “A new Quercus species from the upper Miocene of southwestern China and its ecological significance” has been published in Review of Palaeobotany and Palynology, 193:99-109. http://dx.doi.org/10.1016/j.revpalbo.2013.02.001