Phenotypic variation of Quercus phillyreoides populations on castle peak of South Fujian, China

Abstract

Castle peak is a mountain that resembles the appearance of a castle and protrudes above its surroundings. The phenotypes of Quercus phillyreoides (Fagaceae) populations located on castle peak in the Wushan Scenic Spot of southern Fujian, China, are variegated. It differs significantly from the original form in the presence of persistent yellow-brown stellate hairs on the leaf abaxial surface. To explain this phenomenon, the distribution of Q. phillyreoides populations at the summit of castle peak was investigated, where variant, original, and intermediate forms, as well as typical original populations at the foot of castle peak and another allopatric area, were studied. Differences in micromorphological traits were counted using ANOVA based on leaf epidermal anatomy. Ecological factors were linked with a view to discovering the causes of variation and possible pathways of evolution. The results were as follows: (1) The variant form formed an evergreen broad-leaved scrub community with it as the dominant species on the west side of the summit, and the small patch of scrub on the east side is dominated by the original form, with a few intermediate form individuals within the latter. (2) The densities of single trichome base (STB) and compound trichome base (CTB) in the leaf adaxial epidermis of various populations was very low or even less than 1 No.·mm-2, and the macroscopic expression was glabrous. The mean values of STB density of original, intermediate, and variant forms were increasing in the leaf abaxial epidermis. The mean density of CTB or typical stellate trichome (Tst) on the leaf abaxial epidermis varied from 0.481-1.122 No.·mm-2 to 57.2 No.·mm-2 in the variant form population compared with the original form populations, which macroscopically showed the formation of dense hairs. The stomatal length-width ratio increases from original form (1.187-1.205) to variant form (1.258). (3) ANOVA results showed that variant form leaf abaxial epidermal STB, CTB density and stomatal length-width ratio were significantly increased (larger) than the original form (P0.05). Poor soil, water and heat conditions at the summit of the Wushan castle peak, and combining the background with the obtained results indicate that the variation in the variant Q. phillyreoides leaf abaxial trichomes and stomatal aspect ratio were resistant to drought or temperature extremes. Since pollen flow has not been interrupted, the adaptive evolution of Q. phillyreoides due to specific habitats should be the main reason for this variation compared to geographical isolation. The microscopic traits showed no significant differences (P > 0.05) between the original form population on the top of castle peak and the rest original form populations confirms that the variation has been fixed by long-term selection and the short-term environmental influences play a limited role in shaping the variant traits. This study provides direct evidence that subtropical exceptional granitic landforms promote population differentiation and species formation.

Keywords

• continental island system
• quercus phillyreoides
• leaf microscopic character
• natural selection
• population differentiation