This study examined the morphogenesis of male inflorescences (catkins), staminate flowers, and pollen development in five walnut cultivars over two years. Differentiation of catkins began in spring with the formation of axillary meristems, followed by the successive development of bracts, floral meristems, the perianth, and stamens. Clear genotypic differences were observed in developmental dynamics: the cultivars ‘Sheynovo’ and ‘Champion’ entered the key stages of organogenesis earliest, whereas ‘Elit’ showed the latest differentiation and flowering. During the summer, catkins grew intensively until August, after which their growth slowed considerably. In the following spring, reproductive organ development resumed, with temperature conditions having a marked influence on growth rate. Histological analysis showed that the walnut anther develops through the differentiation of the epidermis, endothecium, middle layers, and tapetum, while microsporogenesis proceeds synchronously within the same microsporangium. Meiosis lasted 6-8 days, the tetrad stage 2-3 days, and the microspore and two-celled pollen stages 7-10 days each. Mature pollen grains were pantopororate, with a spinulate exine. The study was supported by photographic documentation of characteristic stages in the development of catkins, flowers, and anthers, as well as histological and cytological changes in the microsporangia. Strong correlations (r = 0.90-0.98**) were found between developmental stages and the morphometric parameters of catkins and anthers. These results contribute to a better understanding of walnut reproductive biology and may be significant for breeding and cultivar selection according to male flowering phenology.