Abstract: To enhance the efficiency of cross-breeding in Rhododendron, the flowering biological characteristics of three Rhododendron species were studied through field observation and microscopic/submicroscopic analyses. The study focused on flowering dynamics, flower traits, pollen viability, and stigma receptivity at different developmental stages. Results showed that: (1) The three Rhododendron species exhibited asynchronous flowering periods, with R. simsii flowering from mid-March to early April (approximately 20 to 25 d) and single flowers lasting 11–15 d, R. rivulare flowering from mid-April to mid-May (approximately 30 d) and single flowers lasting 12–15 d, and R. moulmainense flowering from mid-April to early May (approximately 15–20 d) and single flowers lasting 8–13 d. (2) The stamen morphology of the three species was similar, although flower colors varied significantly. The pollen in all three species formed compound tetrads, and distinct morphological changes were observed at different flower opening stages. The pollen surface exhibited sticky filaments, which connected the grains into filamentous strings. The highest pollen activity in R. simsii occurred during the petal flat extension period, reaching 82.77%, while R. rivulare achieved 55.66% viability in the bud stage and R. moulmainense reached 81.86% viability in the ready-to-open period. (3) The style morphology was similar across the three species, but notable color differences were present. Throughout development, the anthers and stigmas of all three species displayed wrinkled surface cells, which gradually became plumper, flatter, and eventually disintegrated. Stigma receptivity was initially strong but decreased over time. The stigma of R. rivulare exhibited strong receptivity at the beginning of the ready-to-open stage, while the stigmas of R. simsii and R. moulmainense exhibited strong receptivity during the petal flat extension period. Receptivity could be assessed based on morphological changes. (4) In all three species, the stamens matured before the pistils, with the latter ripening later.