Microsporogenesis and Development of Male Gametophyte in Vitex trifolia var. simplicifolia (Verbenaceae) Relationship between carbohydrate conversion and resistance to sand burial in the stolon of Vitex trifolia var. simplicifolia grown on the Coast in Yantai, China Genetic diversity analysis of Vitex trifolia var. simplicifolia populationswith inter-simple sequence repeats (ISSR) technique